Vegetarian diets do not contain meat, poultry or fish, vegan diets further exclude dairy products and eggs. Vegetarian and vegan diets can vary widely.

In general, vegetarian diets provide relatively large amounts of cereals, pulses, nuts, fruits and vegetables.

In terms of nutrients, vegetarian diets are usually

• rich in carbohydrates, n-6 fatty acids, dietary fibre, carotenoids, folic acid, vitamin C, vitamin E and Mg,
• relatively low in protein, saturated fat, long-chain n-3 fatty acids, retinol, vitamin B12, zinc (Zn),
• vegans may have particularly low intakes of vitamin B12 and low intakes of Ca.

On average, vegetarians and vegans have a relatively low BMI and a low plasma cholesterol concentration, but higher plasma homocysteine concentrations than in non-vegetarians. Overall, the data suggest that the health of Western vegetarians is good and similar to that of comparable non-vegetarians.

In comparison with regular meat eaters, mortality from ischemic heart disease was

• 20% lower in occasional meat eaters,
• 34% lower in people who ate fish but not meat,
• 34% lower in lacto-ovo-vegetarians,
• 26% lower in vegans.

There were no significant differences between vegetarians and non-vegetarians in mortality from the other causes of death examined.

The positive link between bone health and fruit and vegetable consumption has been attributed to the lower renal acid load of a diet high in alkaline-forming fruits and vegetables.

Other important dietary determinants of bone health include micronutrients and bioactives found in fruits and vegetables.

Vegan diets showed statistically significant protection for overall cancer in both genders combined, and for female-specific cancers.

For satiety choose whole fruit over smoothies and juices.

Solid fruits affect feeling of fullness more than pureed fruit or juice. Adding naturally occurring levels of fiber to juice do not enhance satiety.

Gut microbial composition depends on different dietary habits just as health depends on microbial metabolism, but the association of microbiota with different diets in human populations has not yet been shown.

Significant differences were found in gut microbiota between European children (EU) and that of children from a rural African village of Burkina Faso, , where the diet is high in fiber content, and is similar to that of early human settlements at the time of the birth of agriculture.

Burkina Faso children showed a significant enrichment in Bacteroidetes and depletion in Firmicutes, and a unique abundance of bacteria from the genus Prevotella and Xylanibacter, completely lacking in the EU children. Enterobacteriaceae (Shigella and Escherichia) were significantly underrepresented in Burkina Faso children.

In addition, we found significantly more short-chain fatty acids in Burkina Faso children. 

Gut microbiota might have coevolved with the polysaccharide-rich diet, allowing to maximize energy intake from fibers while also protecting from inflammations and noninfectious colonic diseases. 

One study found that 0.85 mg of calcium was lost for each gram (1 g) of protein in the diet. A meta-analysis of 16 studies in 154 adult humans on protein intakes up to 200 g found that 1.2 mg of calcium was lost in the urine for every 1g rise in dietary protein. A small but more focussed study showed a rise of 40 mg in urinary calcium when dietary animal protein was raised from 40 to 80 g. Urinary calcium to dietary protein ratio is 1 mg to 1g. The empirical observation that each 1 g of protein results in 1 mg of calcium in the urine agrees very well with the phosphorus content of animal protein (about 1 percent by weight).

This means that a 40 g reduction in animal protein intake from 60 to 20 g would reduce calcium requirement by the same amount as a 2.3 g reduction in dietary sodium, i.e. from 840 to 600 mg. 

How animal protein exerts its effect on calcium excretion is not fully understood. 

In 2010, the Joint Food and Agriculture Organization / World Health Organization Expert Committee on Food Additives (JECFA) concluded that acrylamide is a human health concern. Certain doses of acrylamide are toxic to animals and humans.

Although acrylamide has known toxic effects on the nervous system and on fertility, the 2002 report by the Food and Agriculture Organization of the United Nations and the World Health Organization (WHO) concluded the intake level required to observe neuropathy (0.5 mg/kg body weight/day) was 500 times higher than the average dietary intake of acrylamide (1 μg/kg body weight/day). For effects on fertility, the level is 2,000 times higher than the average intake.

Acrylamide is a neurotoxin by either oral (in animals) or inhalation exposure (in humans and in animals). Toxic effects are central and peripheral neuropathy causing drowsiness, hallucinations, distal numbness, and ataxia. Recovery is possible after cessation of exposure. 

Acrylamide is typically found in plant-based foods cooked with high heat (e.g., frying, roasting, and baking), not raw plant-based foods or foods cooked by steaming or boiling (below 120 degrees Celsius / 248 Fahrenheit). Potato chips and French fries were found to contain higher levels of acrylamide compared with other foods.

The European Chemical Agency added acrylamide to the list of substances of very high concern in March 2010.

Acrylamide is known to causecancer in animals. It is not clear, as of 2016, whether acrylamide consumption increases people's risk of developing cancer. 

Recommended intake of calcium for adults 19–50 years, in milligrams per day (RDA, recommended dietary allowances based on North American and western European data) is  1000 mga day (1 g).

Example of calcium plant food sources, fruit and seeds: 

• Sesame seeds, whole, roasted - 989 mg calcium / 100 g.
• Chia seeds, dried - 631 mg calcium / 100 g. 
• Figs, dried - 162 mg calcium / 100 g, ~ 600 g figs for 1000 mg (1 g) calcium. 
• Olives, ripe, canned - 94 mg calcium / 100 g.
• Dates, medjool - 64 mg calcium / 100 g.

Vitamin B(12) concentrations of dried green (Enteromorpha sp.) and purple (Porphyra sp.) lavers nori were determined, in micrograms: 

• green nori: 64 - 69 mcg per 100 g of dry weight,
• purple nori: 32 - 25 mcg per 100 g of dry weight.

Non-coenzyme forms (hydroxo and cyano forms) of vitamin B12 predominate in both. 

Recommended dietary amounts (RDAs) for cobalamin, B12, are 2.4 mcg (micrograms) daily, one can cover it with 4 g of dry green nori. 

The dried lavers contained lesser amounts of dietary iodine (~ 4-6 mg per 100 g of dry weight) relative to other seaweeds, suggesting that excessive intake of the dried lavers is unlikely to result in harmful intake of iodine.

These results indicate that the nori are the best source of vitamin B12 among edible seaweeds, especially for strict vegetarians (vegans).