Energy in Food

Introduction

I have learned to count calories from my parents when I was 13-14, and later on from multiple books on "rational nutrition". I returned to the subject later, wondering how can it be that fruit, which almost exclusively supported me and make me want to move quite a lot, are supposedly provide so little energy, or better to say, their estimated caloric value is so low. I never found the answer and this time I was inspired to share my thoughts and questions. Maybe you know the answer.

Origins of food energy

Physicist Paul Doherty, Ph.D. in solid-state physics from MIT:

"Food energy begins its trip up the food chain when light falls on a green plant. The plant stores the energy of sunlight in high-energy chemical bonds. Today, however, some plants are grown under artificial lighting, which is powered in part by nuclear power plants and by geothermal power. Some of the energy stored in the food we eat comes from the nuclear energy stored by exploding supernovas billions of years ago."

Physiologist Len Kravitz:

"It is actually plants that create the primary molecules in food that contain the energy quantified as calories. Green plants create these molecules from carbon dioxide and water by capturing energy from the sun in a process called photosynthesis."

Calorimetry and Digestion

Dr. Samir Bali, Associate Professor of Physics at Miami University:

"Physicists measure the energy content of food by burning the food. To a physicist, a calorie is the heat flow needed to raise the temperature of one gram of water by one degree Celsius. To measure the calorie content of food accurately, scientists use a “bomb calorimeter”. The food sample to be measured is dried and ground into a powder (important point – all water content eliminated). Then it is placed into the bomb calorimeter, a strong metal container surrounded by a water bath. The metal container is pumped full of pure oxygen at 30 atmospheres pressure and the food is ignited. The resulting energy release is fast and violent, just like a bomb. The steel container holds in the explosion. Pure oxygen promotes combustion, and high-pressure oxygen greatly enhances combustion. All of the burnable parts of the dried and powdered food will burn in a calorimeter, leaving just a touch of ash. The calorimeter turns the energy stored in the food into heat flow. The temperature increase of the water and metal of the calorimeter reveals how many calories the food contained. ... Overall, less than 20 percent of the energy contained in food can be converted into work."

Paul Doherty, in Exploring Food Magazine:

To measure the calorie content of food accurately, scientists use a bomb. A bomb calorimeter to be precise. The food sample to be measured is dried and ground into a powder. Then it is placed into the bomb calorimeter, a strong metal container surrounded by a water bath. The metal container is pumped full of pure oxygen at 30 atmospheres pressure and the food is ignited. The resulting energy release is fast and violent - just like a bomb. The steel container holds in the explosion. In air, not all of the peanut burns, but this isn't a problem in the bomb. Pure oxygen promotes combustion, and high-pressure oxygen greatly enhances combustion. All of the burnable parts of a dried and powdered peanut will burn in a calorimeter, leaving just a touch of ash. The calorimeter turns the energy stored in the peanut into heat flow. The temperature increase of the water and metal of the calorimeter reveals how many calories the food contained.

Our organisms are not machines, but very complex bio-systems, adapted to certain qualities and conditions of food. Nobody pumps pure oxygen in our intestinal tract, and such pressure is not created. There is no burning going on. Our bodies oxidizes the food with a low temperature process which is more complicated than the reactions that occur in a fire. In this combustion chemical bonds in food molecules break under the high temperatures, and then combine with oxygen from the air in a reaction called oxidation. Such high temperatures is reached in our intestines. In the calorimeter reaction, fats and carbohydrates are converted to carbon dioxide( CO2) and water( H2O). The oxygen bonds in these compounds have lower energy than the original bonds holding together the fat and carbohydrate molecules. Your body also oxidizes food to release energy and produce carbon dioxide and water. Food reportedly releases the same amount of energy when it is oxidized in the body as when it is burned.

Our digestive process is quite different from the explosion of burned to a powder foods, it is way more complicated. The efficiency of our use of the energy is very important. The structure of bio-material may play a big role in easiness to assimilate the energy and possibility to spend less energy in the process. As we know, the size and type of food molecules make a difference in how a food is digested. Each type of molecule has its own challenge with respect to digestion. But the same may be true for the macro-structure.  The cell is the fundamental unit of life, they are 3 dimensional, with varying sizes and structures. We were evolved consuming food with preserved cell structure.

The dynamic of the process may be of big importance - there are no explosions happening in our bodies, it is step by step procedure, limited in time bu other bodily functions and movement of the food through the intestines.

Food in this calorimeter was changed by drying, but our body acts on moisturized food only: if it contains not enough liquid it will be added to it! Food for me are juicy fresh whole fruits. I do feel differently if I eat, for example some apples, compared to the same amount of dried apples with water. And by the way, how do they dry the food? I bet by heat. It is not raw anymore. One person on a forum said that "the percentage of calories we absorb from raw foodstuffs can be as little as half of the percentage we absorb from the same food when it's cooked." I think it could be the other way around. May be our organisms evolved to convert much more than 20% of evaluable energy from unprocessed food!

We should not forget, that our microflora may play a big role in energy production. It is already been proven, that gut flora influences the body temperature of rodents, it may be the same for us. Symbiotic intestinal flora makes lot's of work for our bodies, and if we care for it, stably providing it with right food, we do not need to use energy on doing the job by ourselves. They can utilize food parts we can not (fibers) and use it in providing us with plenty of nutrients and in fulfillment of other functions (immune, regulatory, etc.).

What if...

• Our body spends a lot of energy on digestion and detoxification, what if by eating only best fresh low toxin-producing food we minimize the need of it?
• What if some preserved elements in this food, such as enzymes, make the digestion much more efficient?
• What if improved breathing provides more oxygen, hence we can use more energy from food? Maybe the top layer of the inside surface of lungs can function more efficiently when eating proper diet (proper functioning cells, less mucus, etc.)?  Or maybe there is more to breathing and we can use some energy from the air somehow? Maybe even from light to some degree?
• What if to maintain leaner body we need less energy - it is quite a effort to carry those extra pounds - it is actually true, according to formulas of caloric intake counting.
• What if our psychological condition - for example, chaotic and agitated thinking versus concentrated state of mind - determines in some way how much energy not only our brain, the biggest consumer (20-25%) uses, but also the whole body, due to level of harmonization of all processes? Stress? 
• What if time of food intake influence the efficiency of assimilating energy? I grew up with old saying always told me: "Eat your morning meal yourself, share your afternoon meal with a friend, give your evening meal to an enemy" - maybe it has something to do with energy consumption and storing? In fact, they say that when you skip breakfast/lunch, your metabolic rate slows down and your blood sugar drops. Scientists have found that the more frequently we eat, the more energy we will expend in digesting the food.
• Correspondingly, what if metabolic rate is a big deal?

And we could continue with "what if"! Do we have answers? No, only partial yet. We know still very little about life - in most cases it is impossible to recreate life partially outside of the organisms in the same conditions, and most of the methods are too invasive to distinguish their influence on living organism, wish abstracts us from understanding how it would function on its own.

What if proportion of macronutriens on our diet impact our energy usage? Humans and animals on low-protein, low-fat diets burn the energy off through very slight increases in thermogenesis, and it is released as body heat instead of becoming body fat, according to T. Colin Campbell, Ph.D.:

"Further research is needed to explain the role of low-protein diets in increased thermogenesis. ... There is some evidence that it could be due to a small amount of a special tissue called brown adipose tissue, although this tissue is not thought to be as significant in humans as in some animals. In addition, most nutritionists regard animal protein as more 'efficient' than plant protein, and one of the efficiencies might result in strong>converting the ingested energy directly to fat."

Adaptive thermogenesis (AT) represents the way the body responds to stress whether it is emotional or environmental. Scientists are still not sure about how much it contributes to total daily caloric expenditure. Many of them think it may be an important factor in explaining why two people can be leading the same type of lifestyle in terms of exercise and diet and yet, have two completely different body types.

"Adaptive thermogenesis may also include spontaneous and unconscious movements like fidgeting and not being able to keep still. Some people are just more "hyper" or nervous than other people who are more placid. The hyper-types may burn more calories."

Scientific studies normally answer only one question, count only few factors, and made under very specific conditions or involve usual people, and not many have been done yet! We are far away from having the whole picture of processes in our body on all levels (physical, chemical, biological, neurological, etc.) and with all its interactions and regulation.

Calories from carbohydrates, proteins and fats

Our food fuel comprises the protein, carbohydrate, fat and alcohol we eat. Our body uses food for energy by turning it into blood sugar, or glucose. Carbohydrates convert most easily into this ready-to-burn fuel, making them your macronutrient of choice for energy eating. We typically burn a mixture of carbohydrates and fat, with the ratio being dependent on meals. Just after meals we burn mainly carbohydrate, while between meals we burn more fat. When insulin levels are low, we burn mainly fat. When they are high, we burn mainly carbs. High insulin levels are typically determined by the type of carbs we eat, but this is another story. 

Like other forms of energy, food energy is expressed in calories or joules. Some countries use the food calorie, which is equal to 1 kilocalorie (kcal), or 1,000 calories.

A calorie in physics is different from a calorie in nutrition. One food calorie (C) is 1,000 times bigger than one physicist's calorie (c). In other words, a food calorie is actually a kilocalorie (Kcal). It is the amount of heat needed to raise the temperature of one kilogram of water by one degree Celcius. Sometimes, the physics calorie is called a small calorie while the food calorie is called a big or large calorie.

One gram of burnt carbohydrates gives an energy value of ~ 4 (4.2) food calories. A gram of protein gives 5.25 calories, but one calorie is deducted because a gram of protein does not oxidize readily and must be subtracted. That gives a final figure for protein of 4.25 - rounded to 4. From the experiment scientists know that one gram of fat contains ~ 9 calories (9.3). The amount of heat generated from fat differs a little for various foods depending on fatty acid content.

One gram of pure alcohol has 7 calories. Does that mean alcohol is better than carbohydrates for us to receive energy? :) Certainly not, and the same is true for other sources of energy. By the way, alcohol calories are burned first, because we cannot store alcohol energy.

Calories from proteins may not be used to supply еnergy (it is better they are not). We do not use any of incoming proteins as they are, we disassemble them into amino acids first and build our own proteins - that process is energy consuming. Fats are also used in the body for other needs then energy and there is many chemical processed going on, depending on how much you eat and what foods.

Digesting some foods may produce unnecessary heat, which is loss of energy. I noticed that when I eat anything cooked I start to feel hot much worse in hot weather, and it feels like my body temperature goes up.

 It takes calories to use the calories in food. Specific dynamic action (SDA) is the amount of calories your body burns when digesting, absorbing and metabolizing a meal. SDA constitutes about 10 % of the total calories burned.

The kind of food you eat affects SDA. Protein elicits the highest SDA, followed closely by carbohydrates.  It has been estimated that the body will use up 25% of calories of protein or carbohydrates to digest those nutrients,  the body will only burn 3% of fat calories to digest and assimilate fat.

T. Colin Campbell, Ph.D., a professor of Nutritional Biochemistry at Cornell University:

"When we treat our body well by eating the right foods, it knows how to partition the calories away from body fat and into the more desirable functions like keeping the body warm, running the body metabolism, supporting and encouraging physical activity or just disposing of any excess. The body is using multiple intricate mechanisms to decide how calories get used, stored or “burned off.” Consuming diets high in protein and fat transfers calories away from their conversion into body heat to their storage form as body fat (unless severe calorie restriction is causing weight loss.)"

Energy absorption in the body

Our digestion system (mouth, esophagus, stomach, small intestine, large intestine) helps us to absorb energy and nutrients from food. 

According to Paul Doherty, our body gets the energy it needs to contract the following way: it begins by breaking food into chemical components during digestion. These components are reassembled into other chemicals, such as glucose, a simple sugar. The circulatory system carries this glucose to the muscle. The lungs take in the oxygen, and hemoglobin transports it via the circulatory system to the muscle. Finally, the oxygen combines with the glucose, producing energy without a flame. The overall reaction is

glucose (C₆H₁₂O₆) + 6O₂ = 6CO₂ + 6H₂O + energy

Part of this energy is released as heat which helps a warm blooded animal stay warm. Most of the rest is used to energize molecules of adenosine triphosphate, or ATP. The energy released by oxidizing one glucose molecule energizes 36 molecules of ATP. The ATP molecules power your muscles. One ATP molecule is used each time a muscle fiber ratchets one step shorter.

In general, the efficiency of muscles is rather low: only 18-26% is converted into mechanical energy. This low efficiency is the result of about 40% efficiency of generating ATP from food energy, losses in converting energy from ATP into mechanical work inside the muscle, and mechanical losses inside the body. The latter two losses are dependent on the type of exercise and the type of muscle fibers being used (fast-twitch or slow-twitch).

If people consume more carbohydrates than they need at the time, the body stores some of these carbohydrates within cells (as glycogen) and converts the rest to fat. Glycogen is a complex carbohydrate that the body can easily and rapidly convert to energy. Glycogen is stored in the liver and the muscles. Muscles use glycogen for energy during periods of intense exercise. The amount of carbohydrates stored as glycogen can provide almost a day's worth of calories. A few other body tissues store carbohydrates as complex carbohydrates that cannot be used to provide energy.

It is maybe important to mention, that only energy absorbed is what really matters, not what you just put through your digestive system. We have no unlimited powers to digest all the food we have eaten, and big part of it goes out only mildly changed - unused. It is not only quantity of food we eat we should care about, but how to get the most of it. The easy rough formula: maximizing gains, minimizing losses - the same as for other systems.

requirements

Average Estimates

UK Department of Health Estimated Average Requirements (EAR) are a daily calorie intake of 1940 calories per day for women and 2550 for men.

These recommendations must be very medium (consider all variations of body builds and energetic needs), and they mean: on average, because our activity and nourishment are vary day to day, so sometimes it can be less, sometimes more.

The National Heart Lung and Blood Institute provides estimates for calorie requirements dependent on gender, age and activity level. Calorie requirements for adult females are 1600-2400 (2,000 to 2,400 calories for ages 19 to 30, 1,800 to 2,200 calories for ages 31 to 50 and 1,600 to 2,200 for ages 51 and above). Daily caloric requirements listed for adult men: 2000-3000 (2,400 to 3,000 for ages 19 to 30, 2,200 to 3,000 for ages 31 to 50 and 2,000 to 2,800 for men age 51 and above). Sedentary individuals require fewer calories than active people.

Calculating calories required per pound of body weight can help estimate daily calorie needs based on age, activity level and desirable body weight. To maintain a current body weight, MedlinePlus gives the following  requirements of desirable body weight 10-18 calorie per pound:

• 10 for obese and sedentary individuals,
• 13 for people over age 55 or who have a low activity level,
• 15 for people who perform regular moderate physical activity and
• 18 for individuals who engage in regular strenuous activity.

The average weight for an adult female is from the National Health and Nutrition Examination Survey (NHANES) conducted from 1999-2002 is 162.9 pounds (73.9 kg) and the average height is ~ 5 feet 3.8 inches (63.8 inches = 162 cm). However, the ideal weight for a female this height and "medium build" would be 126 pounds (57 kg). Thus, according to the suggestions above, the average daily caloric intake for a female should be 1260-2268. For an average male (189.8 pounds, 69.2 inches, 154 lb ideal weight), following the same logic, we would come to the numbers 1540-2772 calories per day.

According to Recommended Dietary Allowance (RDA), females after 50 should reduce their caloric intake by 300 calories (from 2200 to 1900), and men - by 400 (from 2900 to 2300). This is a lot!

As you can see, recommendations may vary significantly dependent not only on your individual characteristics, but also on life phase, lifestyle and the current excessive weight.

Resting rate and activity

Scientists have also discovered that while resting (sitting quietly while reading a book or watching TV), the average person burns one calorie per kilogram of body weight per hour. In terms of oxygen, it is 3.5 milliliters of oxygen per kilogram of body weight per minute. This is what is known as your resting metabolic rate or RMR. 

My body weight in my adulthood (18 years, the half of my life) varied between 45-52 kg, the minimum I reached many times, the maximum - 2-3 times, and most common numbers was 47-48, so I can take my medium weight as 48 kg (106 pounds) for simplicity. Multiplied by 24 hours in a day it is 1152 calories I supposedly minimally need a day, assuming I am very lazy or work on computer and don't exercise.
I usually eat much more that that even on totally sedentary days, but I am gaining a little weight not always depending on how much I eat, and not on how active I am, but on what I eat.

The Harris Benedict Equation is a formula that uses your basal metabolic rate (BMR) and then applies an activity factor to determine your total daily energy expenditure (calories). The only factor omitted by the Harris Benedict Equation is lean body mass. Leaner bodies need more calories than less leaner ones.

Metric BMR Formula  

• Women: BMR = 655 + (9.6 x weight in kilos) + (1.8 x height in cm) - (4.7 x age in years)
• Men:      BMR = 66 + (13.7 x weight in kilos) + (5 x height in cm) - (6.8 x age in years)

You can calculate it here: BMR-Calculator.

Then calculate your daily caloric usage:

• If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2
• If you are lightly active (light exercise/sports 1-3 days/week) : Calorie-Calculati alt= BMR x 1.375
• If you are moderatetely active (moderate exercise/sports 3-5 days/week) : Calorie-Calculati alt= BMR x 1.55
• If you are very active (hard exercise/sports 6-7 days a week) : Calorie-Calculati alt= BMR x 1.725
• If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculati alt= BMR x 1.9

My BMR is 1269 and my activity is between light and moderate, so I used coefficient 1.4 and got 1777 calories a day. Various other calculators I found in internet suggest that I need more than 1920 calories per day. What a difference between 1152 and 1920 - 768 calories! It is more than in a 1 kg (2 pounds) of apples or in a huge 1.5 pound (700g) portion of rice! How reliable could be this information? And by the way, my experience shows that no way this two "meals" could be equal by energy provided and the way my body deals with it. I felt tired and sleepy each time I ate big portion of cooked food, and never like that after fresh fruit.

"Many Americans consume more calories than they need without meeting recommended intakes for a number of nutrients. This circumstance means that most people need to choose meals and snacks that are high in nutrients but low to moderate in energy content; that is, meeting nutrient recommendations must go hand in hand with keeping calories under control."

At least 40 different nations have as well as organizations have published such standards. The RDA are based on scientific knowledge and have been presented by a committee of the Food and Nutrition Board (FNB) of the National Academy of Sciences (NAS). Each individuals food energy intake must equal the energy expended, in order for the person to maintain their body weight.

Calorie Burning

Important, and often overlooked as a source of calorie burning, are activities of daily living (ADL). The number of calories burned varies tremendously among individuals depending on how active or sedentary their daily routine is.

There is a number for estimated calories burnt per hour for many activities, calculated according to the weight of the person. I used two of the best calculators I found and had the following results for myself, how many calories a person of my rather small build burns by activities usual for me:

1. Sleeping 7 hours - 326 cal total.
2. Running with speed 5 miles/hour = 8 kilometers/hour for 75 minutes on some days - 533
   or on other days: high impact aerobic exercise (jumping) for 30 min - ~240 plus 20-30 minutes of other types of exercise: ~150, all together for these non-running days, which are more often: 390 calories. And the total average number between 390 and 533 I think would be ~440, but let's take 500, because often I exercise longer or twice a day.
3. The rest of my day, less than 16 hours, I is filled with activities like typing/writing (~ 12 hours, 53 cal per hour), walking (let's say ~2 hours total, ~180 cal per hour), the remaining 2 hours I give for various activities like studying (93), standing around (60), organizing and washing (110), playing (200), cleaning (226), modern dancing (~264 cal per hour), sex-foreplay (145), gymnastics (182), stretching (192), hatha yoga (140), shopping and putting away groceries (~125), brushing teeth (127), etc. - you've got the idea.
   The mean number per hour for the last 2 hours for these 12 activities is ~153:
   (93+60+110+200+226+264+145+182+192+140+125+127) / 12 = 1864 / 12 = 153(3).
   The total for the whole 16 hours is 1307:
   53x12 + 180x2 + 153(3)x2 = 636 + 360 + 310(6) = ~1307
   
   

This is the total for a day (7 hours sleeping, 1 hour exercise, 16 hours of the rest):

326 + 500 + 1307 = 2307!

It is 530 calories more than I counted previously (1777)! How do they measure that all I'd like to know! Who is to believe?  How am I surviving, eating less? Now I believe even more that there is more energy in fresh whole fruit, or they count wrong.

To lose one U.S. pound (454 g) of fat, one must burn 3,500 more calories than one takes in as food. I don't want to lose any weight, only just a little fat on some parts, but I prefer to replace this weight with that of a muscle tissue. Thus, my caloric intake must be equivalent to my caloric usage.

Another calculator that takes into consideration not only weight but also height, age, lifestyle, and exercise, gave me the result of 2144.0 kcal (food calories).

The difference is not that big. I would need to eat 20-22 bananas a day to provide myself with 2144-2307 calories, or 49-53 apples, or 83-89 tangerines, using the data from the table below. In general, I would need to eat ~ 4,5 kg of fruit daily - I don't do that. And you know what? I cannot imaging eating so much all the time - I would feel horrible, and most of the fruit would go right through me undigested! I tried that in many variations, I know.

There were long periods in my life when I was exercising more intensive (2-4 hours a day) and ate surely less than 2000 calories worth food a day. Again, how could I?!

I can be amazingly efficient on not so much fruit only for quite a long time (many months for sure), being moderately or excessively (for usual understanding) physically active.

I never could eat more than 5-6 bananas at once, and 3 meals would not be enough, 4-5 big meals of bananas, which I don't want. OK, what about apples? 3-6 apples is a nice satisfying meal for me, more seldom feels good, so, should I eat 8-18 apple-meals a day? Or of many other fruits, because the caloric value of many of them per piece is similar or less? And tangerines! That is a big box of them!

All my experience tells me: I don't need so much. I am full of energy with less fruit, it would not be possible for me to be this way if those formulas, measurements and estimations were right at least for fresh whole fruit.

Caloric Tables

I have made a little table to show how little calories are fruit can provide by modern measurements. On the left you can see how with how many calories an average piece of fruit can provide you, and on the right - fruit of the same weight (100g). I analyzed several sources and took the median number in cases where estimates differed:

Caloric value of some fresh fruit per piece and per 100g

Here you can see, that juicy fruit are supposedly very low in energy. The median only for these 15 chosen fruits will be (the right column):

(25+49+39+25+27+30+25+34+60+160+43+107+10+100+36) / 15 = 770/15 = ~ 51

51 calorie per 100g. That's so low, it is difficult to believe for me! I could run on 2-3 kg of fruit, ~ 1000-1500 calories, for months very comfortably, actually very seldom I eat as much as 4-5 kg a day (8-10 pounds of fruit!) or more, mostly on the days when I eat watermelons, but melons are lower in calories: 25 per 100g only, which will make around 1000 calories for 4 kg! (4000/100x25).

1 kg of fruit (2 pounds) is a very nice satisfying meal for me. If you would know me in person, you would not suggest I am anorectic, as guys on the 30bad tend to do if one are disagrees with them - not at all! I eat a lot, whenever I like, and all my body measurements and indexes are very healthy and normal.

And after a couple of handfuls of berries or a melon I feel highly energized, mentally and physically. Is that an illusion or a simple sugar rush, do I "crush" an hour later? No, I can go on for many hours. Why? What are we missing here?

I have not included nuts in this table, because of their high fat content, otherwise the number would be bigger. But from another side I counted the highest on calories dates, bananas and avocado, but I, for example, eat them very seldom. I don't eat dates at all, because I am unable to get fresh ones. I eat bananas and avocados on average 2-3 peaces in 2-3 month, irregularly. 

A variation in caloric intake in 300-1000 calories, would mean the difference in intake of 600-2000 g of juicy fruit! Folks, 2 kg (4 pounds) of fruit make a difference! I could survive on that amount! :)

Actual intake

People

People in USA, Portugal, Austria and Ireland eat on average foods worth more than 3700 calories, daily. But people in Slovakia and Japan, for example, - about 1000 calories a day less! In India and Thailand - around 2450, in Tanzania and Ethiopia - around 1900 calories a day.

Are Portuguese healthier than Indians? Are Americans? Or maybe residents of Thailand are healthier than Ethiopians due to better nourishment? I don't know, I could not find appropriate data, but I don't think so. Japanese and US-Americans have nearly the same life expectancy (80+) despite the huge difference in caloric intake. Same true for people in Morocco, who consume ~ 3000 calories a day. But residents of Tanzania and Ethiopia indeed have much lower life expectancy (50-55+). But it may be an indicator only of overall better life conditions in wealthier countries, where people may allow themselves to eat more.

Today I ate grapes only, a little more than 4 pounds (2 kg). It makes 1330 calories, but I felt totally satisfied, even though I danced the whole evening yesterday (my energy savings in glycogen might have been depleted), but haven't trained today. On some days I eat much more, because I want to, and it feels quite good too, most of the times, depending on the food.

Grate Apes

Experts found that the great apes were burning very few relative calories, despite spending most of their time swinging from structures. Sugary or fatty pulp fruits make up the majority of the animals' diet. Two female orangutans, each weighing about 120 pounds, burned about 1,600 calories a day, several hundred less than a woman of similar weight who is getting moderate amounts of exercise.

Caloric Abundance

Scott Jurek, 36, vegan ultramarathoner, who had three consecutive victories on the 153-mile course between Athens and Sparta, the 2008 Spartathlon, and he holds the 5th-, 6th- and 8th-fastest times in race history, needs 5,000 to 8,000 calories a day:

"I need  and I get that all from plant sources. It’s not hard, either. I like to eat, and I don’t have to worry about weight management. All I need is a high-carbohydrate diet with enough protein and fat."

"The whole issue, is exactly that: getting enough calories. The first thing to worry about isn’t so much what you eat, but how much you eat. You have to take the time to sit at the table and make sure your calorie count is high enough. And when you’re a vegan, to increase your calories as you increase training you need more food. This isn’t an elimination diet but an inclusion diet."

"Despite Dave Costill's excellent research (and fine follow-up investigations by Clyde Williams at the University of Loughborough in England), which showed that endurance athletes who train fairly strenuously need about 4 to 4.5 grams of carbohydrate (CHO) per pound of body weight per day to maintain normal leg-muscle glycogen stores, most endurance athletes don't eat that much CHO."

In research carried out at Xavier and Dayton Universities in Ohio, at the beginning of the study, when the athletes were following their own dietary inclinations, they competed in a short-course triathlon. At this time, the athletes weighed about 154 pounds, possessed 8-per cent body fat, and trained about 11 hours per week. Average daily caloric intake was 2318 calories, with 59 per cent of the calories coming from CHO and 18 per cent from fat. Daily carbo intake was only 2.2 grams per pound of body weight.

The athletes then raised their daily caloric consumption to 3992 calories, boosted carbo intake to 65 per cent of total energy, and heightened daily CHO ingested to 4.2 grams per pound of body weight. They were eating about 1700 more calories per day. That adds up to approximately 47,000 additional calories per person in 4 weeks they followed their new eating plans, enough to prop up about 13 pounds of body fat, but there were no significant gains in weight or percent body fat! The general training scheme during this four-week period was the same. At the end they completed a second short-course triathlon. The athletes improved their performance times by an average of almost 8 % (from 5 hours, 25 minutes to 5 hours flat)!

In this experiment is unclear what helped higher performance: more carbohydrates or more calories? I would assume, that more carbs, that helped maintain glycogen stores. Thus, the study says us that endurance athletes should take enough carbohydrate if they still don't.

Calorie restriction

Caloric restriction (CR), a dietary regimen that restricts calorie intake, when not associated with malnutrition, has been shown to improve age-related health and to slow the aging process in a wide range of animals and some fungi. It has nothing to do with starvation, the needed amount of energy in food is always met.

A small study of long-term CR practitioners in the US at the Washington University School of Medicine studied the effects following a calorie-restricted diet of 10-25% less calorie intake than the average Western diet, which is over caloric. Body mass index (BMI) was significantly lower in the calorie-restricted group when compared with the matched group; 19.6 compared with 25.9.

Subjects in the calorie restriction group had total and low-density lipoprotein (LDL) cholesterol levels comparable to the lowest 10% of the population in their respective age groups; high-density lipoprotein (HDL) cholesterol levels in the 85th to 90th percentile for middle-aged men; and triglyceride levels lower than more than 95% of Americans in their twenties.

John O. Holloszy, MD, from Washington University School of Medicine in St. Louis, Missouri:

"It's very clear from these findings that calorie restriction has a powerful, protective effect against diseases associated with aging. We don't know how long each individual actually will end up living, but they certainly have a much longer life expectancy than average because they're most likely not going to die from a heart attack, stroke, or diabetes."

The calorie-restricted individuals were actually aged between 35 and 82 years. Both systolic and diastolic blood pressure levels in calorie-restricted group were remarkably low, about 100/60, values normally found in 10-year-old children. Usually, systolic blood pressure rises with age reliably, partly because the arteries are hardening.

"The calorie-restricted group also fared much better than the control group in terms of average blood pressure (100/60 vs. 130/80 mm Hg), fasting glucose, fasting insulin (65% reduction), body mass index (19.6 ± 1.9 vs. 25.9 ± 3.2 kg/m²), body fat percentage (8.7% ± 7% vs. 24% ± 8%), C-reactive protein, carotid IMT (40% reduction), and platelet-derived growth factor AB."

Luigi Fontana, MD, PhD, from Washington University:

"These effects are all pretty dramatic. For the first time, we've shown that calorie restriction is feasible and has a tremendous [effect] on the risk for atherosclerosis and diabetes."

Although most studies conducted showed that these diets can improve longevity and health in the long term, the effects of calorie restriction on humans is still controversial. Some studies on humans revealed a number of benefits of calorie restriction but also major side effects such as loss of muscle mass, muscle strength and loss of bone. 

Although calorie restriction may provide quick weight loss, several studies have shown that the body adjusts to the new diet in more or less half a year. Researches argue that people who have little body fat do not use this method of losing weight and rather exercise more because calorie restriction in this case can be harmful.

"A one-year study published in the July 2007 issue of the AmericanJournal of Physiology, Endocrinology and Metabolism compared the effects of an extremely low-calorie diet and exercise on coronary heart disease risk factors in lean and overweight middle-aged adults. Both calorie restriction (consuming 20 percent fewer calories) and exercise (expending 20 percent more calories) lowered bad (LDL) cholesterol, raised good (HDL) cholesterol levels, and improved insulin resistance, but only calorie restriction led to significant declines in risks associated with heart disease and heart attacks."

"Several studies conducted in this sense revealed that dieters who restricted calories for 12 months had lower muscle mass and a reduced capacity to perform exercise compared with those who lost similar amounts of weight from exercise alone. Another study concluded that individuals who lost weight with the help of the calorie restriction diets are more prone to develop a loss of bone at the level of hip and spine, the area most at risk for bone fractures."

I wonder, what if those studies being made with at least raw food diet? Or with fat restriction, or just on vegan diet?

Were those people on the restricted diet exercising at all? What about comparing people on restricted and unrestricted diets exercising with the same intensity? And what about quality of muscle tissue, not only about its mass? Every good dancer can tell you how important it is to keep your muscles lean but strong and flexible for better performance and teach you special techniques to achieve it. I saw perfectly able skinny athletes and bulky bodybuilders, who were going out of breath on the second kilometer by running.

"Caloric Restriction in non-obese people translates into less oxidative damage in muscle cells, according to a new study by Anthony Civitarese, Eric Ravussin, and colleagues (Pennington Biomedical Research Center)."

Recent study published in the June 2007 issue of Rejuvenation Research found no significant connection between the diet and cognitive impairments.

John O. Holloszy of the Washington University School of Medicine, in St. Louis, Missouri:

"It’s dangerous to decrease calorie intake, or reduce weight after age 65, when one is already losing muscle and lean tissue. Still,  most people would benefit tremendously from even moderate calorie restriction."

Dave Fisher, a "calorie-restrictor":

"There is evidence that DNA repair is more efficient on a CR diet. The theory is that, in times of famine, the body puts more resources into keeping itself alive. When there's plenty of calories around, the body goes into breeding mode. It doesn't bother to repair itself, because, when you can reproduce and pass on your genes, you – as an individual – no longer matter that much."

Low protein

If fruit flies and rodents are fed special diets with less amino acids - the building blocks of proteins - they can eat as many calories as they want and still live longer. Cutting intake of the amino acid methionine lengthens life to a similar degree as calorie restriction. Proteins in meat and other animal products have high levels of methionine.

  A molecule called TOR has been found to set off a chain of reactions inside cells that boost cell growth at the expense of longevity. Blocking TOR increases lifespan in all organisms studied to date, including yeast and mice. The most potent activators of TOR are amino acids, building blocks of proteins.

Dietary restriction (DR) is a robust nongenetic, nonpharmacological intervention that is known to increase active and healthy lifespan in a variety of species. Despite a variety of differences in the protocols and the way DR is carried out in different species, conserved relationships are emerging among multiple species. 2009 saw the field of DR mature with important mechanistic insights from multiple species. A report of lifespan extension in rapamycin-treated mice suggested that the TOR pathway, a conserved mediator of DR in invertebrates, may also be critical to DR effects in mammals. 2009 also saw exciting discoveries related to DR in various organisms including yeast, worms, flies, mice, monkeys and humans.

It's good news for people on low-protein diets, like vegans. In 2007 it had been shown showed that vegans have lower levels of insulin-like growth factor 1 (IGF-1) than meat-eaters.

Protein restriction is much less difficult to maintain than calorie restriction. But maybe you would want to try both.

Stress and Free Radicals

There is a theory that says that calorie restriction reduces the amount of glucose that comes into cells over time, curtailing production of free radicals in the mitochondria. The other theory says that dietary restriction increases life span because it imposes mild stress on the organism: the organism that learns to exist on a curtailed diet is better able to cope with more severe stress at the cellular level and to resist diseases that are associated with certain types of stress.

Leonard Guarente of the Massachusetts Institute of Technology in Cambridge has suggested that an organism responds to food scarcity—stress—by slowing aging and reproduction, so as to survive and be able to reproduce when conditions improve. The key to this adaptive response, Guarente and others believe, is a set of genes known as sirtuins, especially SIR2 that is associated with metabolism, that help cells to withstand stress by regulating the pace of aging based on the availability of nutrients. Studies have shown that, when stimulated, sirtuins can extend the life span of cells, and of worms. What’s more, this effect is greater when calories are cut.

Guarente:

"We don’t know that this is the only gene that may be responsible for regulating so many fundamental processes tied to aging. But it does seem to be the first that exerts so many effects related to life span in so many organisms."

Other scientists, including David Sinclair, now at Harvard Medical School in Boston, Massachusetts, also think that SIR2 is involved, but they hypothesize that the key lies in biological processes involving a vitamin B precursor called nicotinamide and a gene called PNC1. Sinclair and others also are studying resveratrol—an antioxidant abundant in grapes, red wine, and other plants—that also activates sirtuin proteins in many organisms.

Resume

Complexity of chemical processes in our body and insufficient quality of known methods of measuring energy in food makes for me the caloric intake counting not very reliable tool in determining how much and what should I eat. It is a good thing to know for orientation though.

To advise people to get every day not less and no more than a certain number of calories without any respect to individual needs (age, gender, size, build, weight, level of physical activity, special situations) - may be improper. To advise not to listen to their own bodies and its messages, like hunger and thirst, to disregard this "first hand insider information" from most loyal source, own body, but instead listen to a chosen experts advise only, seems to be unacceptable to me. 

Our goals in life may differ: somebody wants highest performance now, somebody wants to live as long as possible, and the methods of achieving them may be exclusive to each other - you must either choose or search for a perfect balance.

I don't think I have right to recommend anything, I try to make people thinking for themselves, providing them with most reliable data and some example. I think there are too many factors to count to recommend anything general on this point. As I have shown in this article, even sophisticated methods of counting vary way too much in results to be reliable.

My recommendation if any would be:

Eat as much fresh fully ripe juicy fruit as you want , better organic. Chose types of fruit you want, eat slowly enough to enjoy it. For people just starting the new diet I would recommend to eat even more than they think they should or feel like, because your body and mind are not adapted to the new diet yet, and you may not instinctively know how much you need. Appropriate satiation responses and adequate eating behavior develop with years of permanent practice.

What do you think?