Plant-based Diets

  • According to the American Dietetic Association a vegetarian diet is defined as one that does not include meat (including fowl) or seafood, or products containing those foods.
  • Vegans, in addition to being vegetarian, do not use other animal products and by-products such as eggs, dairy products, honey, leather, fur, silk, wool, cosmetics, and soaps derived from animal products.
  • Features of a vegetarian diet that may reduce risk of chronic disease include lower intakes of processed foods, decreased saturated fat and higher intakes of fruits, vegetables, whole grains, nuts, soy products, fiber, and phytochemicals. (J Am Diet Assoc. 2009;109:1266-1282).

There are different terms associated with those who eat “plant-based” diets. A brief definition of terms can be helpful:


  • Vegans (total vegetarians): Do not eat meat, poultry, fish, or any products derived from animals, including eggs, dairy products, and gelatin.
  • Lacto-ovo vegetarians: Do not eat meat, poultry, or fish, but do eat eggs and dairy products.
  • Lacto-vegetarians: Eat no meat, poultry, fish, or eggs, but do consume dairy products.
  • Ovo-vegetarians: Eat no meat, poultry, fish, or dairy products, but do eat eggs.
  • Partial vegetarians: Avoid meat but may eat fish (pesco-vegetarian, pescatarian) or poultry (pollo-vegetarian).

Scientific evidence reveals a health advantage to vegetarian diets.   Studies show vegetarian diets can prevent or favorably influence cardiovascular disease, hypertension, diabetes, some cancers, osteoporosis, dementia, kidney disease, diverticular disease, gallstones and inflammatory diseases such as rheumatoid arthritis or multiple sclerosis.

The benefits of plant-based nutrition may arise from lower intakes of animal protein (and particularly processed meats), as well as, higher intakes of complex carbohydrates, dietary fiber, magnesium, folic acid, vitamin C and E, phytochemicals (plant chemicals) such as carotenoids and flavonoids.  As a result, vegetarians have been shown to have lower blood pressure, lower weights, lower cholesterol levels and longer disease free survival. However, there still aren’t enough data to say exactly how a vegetarian diet influences long-term health. It’s difficult to separate the influences of vegetarianism from other practices that vegetarians are more likely to have, such as not smoking, not drinking excessively, and exercising regularly.

Studies support health benefits

Heart disease: An analysis of five studies (meta-analysis), involving approximately 76,000 subjects from the USA, the UK and Germany, over a period of nearly 11 years, reported that vegetarians had a 24 % reduction in mortality from heart disease compared with regular meat-eaters.  Further characterization of the vegetarian cohorts within that analysis found that the greatest reductions in heart disease death (mortality reduced by 34%) were observed in individuals eating fish but no meat and in lacto-ovo-vegetarians when compared with regular meat-eaters. Furthermore, occasional meat-eaters demonstrated a 20% reduction in heart disease when compared with regular meat eaters.

  • For heart protection, it’s best to choose high-fiber whole grains and legumes, which are digested slowly and have a low glycemic index — that is, they help keep blood sugar levels steady. Soluble fiber also helps reduce cholesterol levels. Refined carbohydrates and starches like potatoes, white rice, and white-flour products cause a rapid rise in blood sugar, which increases the risk of heart attack and diabetes (a risk factor for heart disease).
  • Nuts are also heart-protective. They have a low glycemic index and contain many antioxidants, vegetable protein, fiber, minerals, and healthy fatty acids. The downside: nuts pack a lot of calories, so restrict your daily intake to a small handful (about an ounce). The upside: because of their fat content, even a small amount of nuts can satisfy the appetite. Walnuts, in particular, are a rich source of omega-3 fatty acids, which have many health benefits. Even so, fish are the best source of omega-3s, and it’s not clear whether plant-derived omega-3s are an adequate substitute for fish in the diet. A study presented in 2008 at the Fifth International Congress on Vegetarian Nutrition suggests that omega-3s from walnuts and fish both work to lower heart disease risk, but by different routes. Walnut omega-3s (alpha-linolenic acid, or ALA) help reduce total cholesterol and LDL (bad) cholesterol, while omega-3s from fish (eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA) lower triglycerides and raise HDL (good) cholesterol levels.

Cancer: Hundreds of studies suggest that eating lots of fruits and vegetables can reduce the risk of developing certain cancers, and there’s evidence that vegetarians have a lower incidence of cancer than nonvegetarians but the differences aren’t large. A vegetarian diet can make it easier to get the recommended minimum of five daily servings of fruits and vegetables, but a purely vegetarian diet is not necessarily better than a plant-based diet that also includes fish or poultry. For example, in a pooled analysis of data from the Oxford Vegetarian Study and EPIC-Oxford, fish-eaters had a lower risk of certain cancers than vegetarians.

If you stop eating red meat-especially if it is processed (whether or not you become a vegetarian), you’ll eliminate a risk factor for colon cancer. According to a 2007 report from the World Cancer Research Fund/American Institute for Cancer Research, red meat consumption is the only “convincing” dietary association with colon cancer. It’s not clear whether avoiding all animal products reduces the risk further. Vegetarians usually have lower levels of potentially carcinogenic substances in their colons, but studies comparing cancer rates in vegetarians and nonvegetarians have shown inconsistent results.

Type 2 diabetes: Research suggests that a predominantly plant-based diet can reduce the risk for type 2 diabetes. In studies of Seventh-day Adventists, vegetarians’ risk of developing diabetes was half that of nonvegetarians, even after taking BMI into account. The Harvard-based Women’s Health Study found a similar correlation between eating red meat (especially processed meats, such as bacon and hot dogs) and diabetes risk, after adjusting for BMI, total calorie intake, and exercise.

Bone health: Some women are reluctant to try a vegetarian diet — especially one that doesn’t include calcium-rich dairy products — because they’re concerned about osteoporosis. Lacto-ovo vegetarians (see “Varieties of vegetarians”) consume at least as much calcium as meat-eaters, but vegans typically consume less. In the EPIC-Oxford study, 75% of vegans got less than the recommended daily amount of calcium, and vegans in general had a relatively high rate of fractures. But vegans who consumed at least 525 milligrams of calcium per day were not especially vulnerable to fractures.

  • Certain vegetables can supply calcium, including bok choy, broccoli, Chinese cabbage, collards, and kale (spinach and Swiss chard, which also contain calcium, are not such good choices, because along with the calcium they have oxalates, which make it harder for the body to absorb calcium.) Moreover, the high potassium and magnesium content of fruits and vegetables reduces blood acidity, lowering the urinary excretion of calcium. Some research suggests that eating too much protein (in particular, animal protein) is bad for bones because it has the opposite effect.
  • People who follow a vegetarian and especially a vegan diet may be at risk of getting insufficient vitamin D and vitamin K, both needed for bone health. Although green leafy vegetables contain some vitamin K, vegans may also need to rely on fortified foods, including some types of soy milk, rice milk, organic orange juice, and breakfast cereals. They may also want to consider taking a vitamin D2 supplement (vitamin D3 comes from animals).

Vegetarian diet health concerns

Avoiding non-plant based sources of proteins may require attention to some details.

  • Plant-based foods may be deficient in one or more essential amino acids needed for normal growth and repair. Essential amino acid deficits of any particular plant food can often be overcome by combination with a complementary plant food. For example legumes combined with grains offer complementary amounts of amino acids and together provide a “complete” protein source (grains are generally low in the amino acid lysine and high in methionine while legumes are low in methionine and high in lysine).

The typical protein intakes of lacto-ovovegetarians and of many vegans nevertheless, appears to meet and exceed requirements with attention to “complementary” plant nutrition. Plant-based proteins therefore may be considered “incomplete” proteins since all essential amino acids are not be found with the one exception: quinoa. This unique gluten-free pseudograin contains all eight essential amino acids, making quinoa a complete protein food.

Other specific issues to be consider

  • A possible risk of vitamin B12 deficiency is present since this is a vitamin of animal origin and consequently a B12 supplement is advisable.
  • Vegetarian diets are generally rich in the essential omega-6 fatty acid called linoleic acid (LA) and the omega-3 fatty acid alpha-linolenic acid (ALA) another plant derived essential fatty acid (an essential fatty acid is one that cannot synthesized by humans). However, diets that do not include fish, eggs, or generous amounts of algae generally are low in the two specific long-chain omega-3 fatty acids called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Both of these particular omega-3s, EPA and DHA are important for cardiovascular health as well as eye and brain development. The body does not significantly convert alpha-linolenic acid (ALA), to the long-chain form and both EPA and DHA blood levels are lower as a result of a lack cold-water fish intake -the richest sources of these important omega3s. Those with increased requirements of omega-3 fatty acids, such as pregnant and lactating women, or those with known cardiac disease may benefit from DHA-rich microalgae or other omega-3 supplements rich in EPA and DHA.
  • The bioavailability of zinc from vegetarian diets is also lower than from nonvegetarian diets, mainly due to the higher phytic acid, a compound that inhibits zinc absorption (by chelating, or binding, this mineral in the GI tract). The zinc in whole-grain products and plant proteins is less bioavailable due to their relatively high content of phytic acid. Zinc requirements (as well as other minerals like iron and calcium) for some vegetarians whose diets consist mainly of phytate-rich unrefined grains and legumes may be higher and a multivitamin plus mineral supplement can be considered. Calcium fortification for those children who do not drink milk or use dairy products must be considered for optimal bone growth especially in adolescent girls.
  • Iron is another mineral that is naturally present in many foods, fortified in some foods, and available as a dietary supplement and is an essential component of hemoglobin, the protein in blood that carries oxygen to our tissues. Iron is important especially in menstruating females: the iron in plant foods is called nonheme iron, which is sensitive to variable absorption into the body. Due to variable absorption of plant-derived iron in vegetarians (lower bioavailability of iron from a vegetarian diet), the recommended iron intakes for vegetarians are nearly 2X those of nonvegetarians. Inhibitors of iron absorption include phytates, calcium, and the polyphenolics in tea, coffee, herb teas, and cocoa. Fermentation processes, such as those used to make miso and tempeh, improve iron bioavailability as can organic acids found in fruits and vegetables and vitamin C can enhance iron absorption and reduce the inhibitory effects of phytate.

Anemia and Iron

More on anemia is a condition with too little blood hemoglobin, that can interfere with normal health and reduce exercise performance and even cognitive function. Low iron is one of many causes of anemia and the major worldwide cause of iron deficiency anemia is related to dietary iron deficiency. Many dietary staples, such as bread, and whole grains and seeds contain inhibitors of iron that markedly diminish the absorption of the iron supplement (phytates). Tips for taking iron supplements: foods that you should not eat at the same time as you take your iron include high fiber foods, such as whole grains, raw vegetables, and bran, foods or drinks with caffeine. Milk, calcium and antacids should not be taken at the same time as iron supplements. Black or pekoe teas contain substances that bind to iron (phytates) so it cannot be used by the body. Vitamin C supplement or drinking orange juice can increase absorption. Black stools are normal when taking iron tablets but if the stools are tarry looking as well as black, if they have red streaks, or if cramps, sharp pains, or soreness in the stomach occur, talk to your health care provider immediately.

Dietary iron has two main forms: heme and nonheme and plants and iron-fortified foods only contain nonheme iron. Meat, seafood, and poultry contain both heme and nonheme iron. The best sources of iron include: dried beans, dried fruits, eggs (especially egg yolks), eron-fortified cereals, Liver, Lean red meat (especially beef), Oysters, Poultry, dark red meat, Salmon, Tuna, whole grains, Reasonable amounts of iron are also found in lamb, pork, and shellfish. Surprisingly 3 oz. of cooked top sirloin contains only 2.0mg of iron (156 calories) compared to a similar amount of canned and drained clams with more than ten-times the amount of iron at 23.8 mg (126 calories).

Too much iron may be related to the genetic disorder called hemochromatosis that affects the body’s ability to control how much iron is absorbed. This leads to too much iron in the body. Treatment consists of a low-iron diet, no iron supplements, and phlebotomy (blood removal) on a regular basis. Iron deficiency, on the other hand, is possible in the following groups: women who are menstruating, especially if they have heavy periods, women who are pregnant or who have just had a baby, long-distance runners, people with gastrointestinal bleeding (or a bleeding ulcer, hemorrhoids), people who frequently donate blood, people with gastrointestinal conditions that make it hard to absorb nutrients from food. Infants are born with enough iron to last about six months and an infant’s additional iron needs are met by breast milk usually until about 4-6 months of age; infants if not breastfed require an iron supplement or iron-fortified infant formula.


Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes. We agree with Michael Pollan’s recommendation: “Eat food. Not too much. Mostly plants.” It’s no wonder that fruits and vegetables are the cornerstone of the dietary patterns including the AHA 2020 initiative that are most associated with health.

Key TJ, et al. Mortality in vegetarians and non-vegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J ClinNutr, 1999: 70, Suppl. 3, 516S–524S.