Examples: Dean Ornish, Mark Bittman. Improved health is among the many reasons one might choose a vegetarian diet, so let's take a closer look at this way of eating to see if it is healthier than diets that include meat.
FOODS All foods except for meat are permitted. Dairy and eggs allowed.
Unclear. Studies of vegetarian diets have unfortunately not been conducted in a way that can prove that simply removing meat from the diet provides any health benefits (see below).
Vitamin B6 deficiency
Vitamin B12 deficiency
Iron and other mineral deficiencies
Omega-3 fatty acid deficiency
Lacto-ovo-vegetarians do not eat animals, but they do eat animal products, such as dairy products and eggs. Both Dean Ornish and Mark Bittman allow for some flexibility in their dietary recommendations, but both believe that plant foods are healthier than animal foods and that people are better off eating as little meat and animal fat as possible. They also both strongly advocate (as do I) for a whole-foods diet, avoiding refined and processed foods.
Are vegetarian diets healthier?
Vegetarian diets, like all diets, can vary widely in quality, depending on food choices, which is why it is very difficult to say whether vegetarians as a group are healthier than meat-eaters. For example: a vegetarian whose diet is based on whole foods and is careful to get enough protein is eating a much healthier diet than a vegetarian who eats junk food all day long and doesn’t count protein grams. Just because a food contains no meat doesn’t mean it is healthier. There is no shortage of extremely unhealthy vegetarian foods. Most junk food is meatless—candies, cakes, cookies, white bread, chips, ice cream, etc.–are all free of meat but loaded with refined carbohydrates and are very poor in nutritional value. Some varieties of these types of foods may be very high in artificial ingredients, as well.
The many studies I have looked at that claim plant-based diets are superior to omnivorous diets have four flaws:
1) Nearly all studies done to date have been epidemiological studies, and therefore cannot prove that vegetarian diets are healthier because they do not contain meat.
2) Vegetarians, probably because they tend to be more health-conscious as a group, also tend to smoke less, drink less, and exercise more than omnivores. The vast majority of studies of vegetarians do not properly control for these variables. Therefore, even if vegetarians appear healthier in some respects than meat-eaters, it may or may not have anything to do with their avoidance of meat.
3) Epidemiological studies of vegetarians, including the largest studies ever done in the UK, USA, and China (yes, the famous China Study), unfortunately do not take refined carbohydrate consumption into consideration as a potential risk factor for disease.
4) The very few clinical trials (experiments) that have been conducted comparing the health effects of a plant-based diet to an omnivorous diet not only remove meat from the diet; they also removed most fat and refined carbohydrate, as well. Therefore there is no way to know whether the health of people in the vegetarian study groups improved because they were instructed to avoid meat, fat, and/or refined carbohydrate.
Can vegetarian diets help with weight loss?
While many studies of vegetarians find that they tend to weigh less on average than omnivores, there is no evidence that people who avoid meat are more successful at losing weight than people who eat meat. The few properly-designed studies that have been done find no difference in weight loss between vegetarian diets and meat-inclusive diets. This suggests that there are other reasons why many vegetarians weigh less than meat-eaters that have nothing to do with avoidance of meat (i.e. exercise habits or healthier food choices).
A vegetarian diet may or may not be higher in fiber than a meat-based diet—it depends on food choices. A high-fiber diet can be more filling, and therefore can help some people eat less, which may help with weight loss in some cases. A vegetarian who doesn’t eat many fruits, vegetables, or whole grains, and instead prefers a diet high in dairy products, sweets and refined baked goods is eating a very low-fiber diet, whereas a meat-eater who eats lots of fruits, vegetables, and whole grains is eating a very high-fiber diet. However, since most vegetarians eat lots of plant foods, their diets do tend to be relatively high in fiber.
Some people believe that vegetarian diets are better for weight loss because they are lower in fat, and therefore lower in calories. However, fat, whether it comes from animal or plant sources, contains the same number of calories (beef fat and olive oil both contain 9 calories per gram). A vegetarian diet is also not necessarily low in fat or calories. The amount of fat and calories in a vegetarian diet depends on food choices. It is certainly possible to eat a very high-fat diet as a vegetarian: cheese, vegetable oils, nuts, avocadoes, chocolate, and ice cream are all examples of very high-fat vegetarian foods. Even if all vegetarians ate a low-fat diet, it would not necessarily lead to weight loss, because the evidence tells us that low-fat diets are no better for weight loss than diets with the same number of calories that are higher in fat.
Do vegetarian diets improve cholesterol levels?
There are numerous studies claiming that vegetarian diets improve cholesterol profiles; unfortunately they are designed in such a way that lifestyle factors other than meat avoidance (avoidance of refined carbohydrate, for example) may be responsible for those changes. However, even if we assume that avoiding meat lowers “bad cholesterol”, this will not necessarily improve health.
First of all, cholesterol levels are misleading—having lower LDL (“bad cholesterol”) does not necessarily protect you from heart disease or other health problems, and having higher LDL cholesterol does not necessarily increase your risk for heart disease or other health problems (see: cholesterol).
Secondly, since cholesterol comes only from animal foods, vegetarian diets may or may not be lower in cholesterol than omnivorous diets, depending on how much egg and dairy are included in the diet.
Thirdly, eating a low cholesterol diet will not necessary lead to low cholesterol blood levels and eating a high cholesterol diet will not necessary lead to high cholesterol levels; the relationship between cholesterol in food and cholesterol in your bloodstream is not straightforward (see cholesterol).
Do vegetarian diets treat or prevent heart disease?
Epidemiological studies tell us that vegetarians have a lower risk of heart disease—about 24% lower—than the general population. Evidence from clinical studies so far, including evidence from the well-known Ornish clinical trials, tells us that vegetarian diets can reduce risk factors for heart disease and improve the health of the heart—however, the diets tested were not only meatless, they were also very low in fat and very low in refined carbohydrates. Therefore it is impossible to know whether the vegetarian diets studied were better for the heart because they did not include meat, because they were extremely low in fat, or because they excluded refined carbohydrates.
Do vegetarian diets treat or prevent cancer?
The majority of epidemiological observations find no difference in cancer rates between vegetarians and omnivores but the quality of evidence is generally poor on this topic. In practice, it would be very difficult to design a human experiment that could answer this question.
Prof T Colin Campbell is probably best known for having written The China Study, a very popular book implying that animal foods cause cancer, heart disease, diabetes, and obesity. While a detailed critique of this study is beyond the scope of this section, suffice it to say for now that the China Study was a) an epidemiological study, and therefore incapable of proving that any dietary factor caused or prevented any health problem; and b) did not take refined carbohydrate into account as a potential risk factor for chronic disease.
Do vegetarian diets help with constipation or improve digestive health?
Constipation and the general health of the digestive tract are ultimately about digestibility. When foods are easily broken down and absorbed, they tend not to cause constipation. Dairy products, and all plant foods except for fruits, are somewhat difficult to digest and absorb, whereas meat and fat are relatively easy to digest and absorb. Since vegetarian diets are based on plant and dairy foods, and since most omnivores also eat lots of plant and dairy foods, digestive issues can be problematic for both groups.
Fiber does not necessarily help with constipation (see: fiber) —it depends on your individual chemistry and on what else you are eating. Vegetarian diets may or may not be higher in fiber than meat-based diets—it depends on food choices.
Do vegetarians live longer?
All we have are epidemiological observations to attempt to answer this question, but these do not show any difference in mortality between vegetarians and omnivores.
Do vegetarians get enough protein?
Protein deficiency is quite uncommon among lacto-ovo vegetarians, and is easily avoided by counting protein grams.
Vitamin deficiencies in vegetarians
Vitamin B12 is only found in animal foods, therefore B12 deficiency may occur. Potential consequences of B12 deficiency include anemia, fatigue, difficulty concentrating, and depression. B12 deficiency is easily remedied with supplements.
The form of Vitamin B6 that is found in most plant foods is less bioavailable than the forms found in animal foods, therefore some vegetarians may not get enough B6 from the foods they eat. Severe deficiencies are uncommon, but symptoms of significant B6 deficiency include mouth ulcers and neurological symptoms, including irritability and depression.
Vitamin D deficiency is more common in vegetarians because the only other source of Vitamin D other than sunlight exposure is animal foods. However, most milk in the U.S. is fortified with Vitamin D, so vegetarians who drink milk or eat fortified dairy products are at lower risk. Vitamin D is also available in supplement form. Potential consequences of vitamin D deficiency include rickets (soft bones) and muscle weakness.
Mineral deficiencies in vegetarians
Plant foods are naturally high in “anti-nutrients”, like cellulose, phytates and tannins that interfere with the absorption of minerals (see : vegetables). Iron, zinc and calcium deficiencies are most common. Omnivores who eat lots of plant foods are also at risk for these deficiencies.
Iron deficiency is best known for causing mild anemia and fatigue, but iron is also required for proper function of the brain, and deficiency can cause memory and other cognitive problems, particularly in the very young.
Iron deficiency (and associated mild anemia) is common among vegetarians; this is primarily because plant sources of iron are harder to absorb. Vegetable iron (or “non-heme” iron), is 8 times less available to the body than “heme” iron, the form of iron found in meat. Milk and eggs, because they are animal products, do contain bioavailable “heme” iron, but there are problems with both of these foods as iron sources:
- Dairy products are extremely low in iron.
- The iron in eggs is concentrated in the egg yolk, which unfortunately also contains a protein called “phosvitin” which reduces iron absorption by nearly 30%.
So, what is a vegetarian to do?
Traditional iron supplements can be irritating to the gastrointestinal tract (constipation is a common side effect), and may not even be that helpful, since they are also in the non-heme form and are therefore difficult to absorb. If you do take non-heme iron supplements, you only need to take them 2-3 times per week, as your intestinal cells can only absorb so much before they become saturated with iron and stop taking any more in. Also, avoid taking calcium supplements with your iron because calcium interferes with iron absorption, too. Heme iron is available as a supplement, but does come from animal sources. Vitamin C supplements can also improve iron absorption.
Zinc deficiency can increase susceptibility to infection and skin problems.If you need supplemental zinc, use small doses, as too much zinc can cause nausea and can also cause copper deficiency.
If you need supplemental calcium, choose calcium citrate over other forms, as it is easier to absorb.
How do vegetarians get omega-3 fatty acids?
Essential omega-3 fatty acid levels can be low in vegetarians. Of the three essential omega-3 polyunsaturated fatty acids—ALA, DHA, and EPA, only ALA is found in traditional plant foods, such as flaxseed and walnuts. Unfortunately, only a very small amount of ALA (about 5%) can be converted to DHA, so dietary deficiencies of DHA can occur. Varying amounts of DHA can be found in eggs, depending on how the hens are fed. Omega-3 fatty acid supplements are now available from (vegan) microalgae sources.
BOTTOM LINE ABOUT VEGETARIAN DIETS:
I find no evidence that simply removing meat from the diet improves health, however there are many other reasons why some people choose not to eat meat, including religious, ethical, environmental, and economic reasons.
Many studies of vegetarians find that they tend to weigh less and that they have a lower risk of heart disease; however because they also tend to smoke less, drink less alcohol, and exercise more (and may also eat less refined carbohydrate), we do not know which lifestyle factors are responsible for these observations.
If you tolerate plant foods well, count protein grams, and eat a varied diet, a vegetarian diet may be a reasonable option for you. To make this diet (or any diet) healthier, avoid processed foods and refined and high glycemic index carbohydrates.
Eating a vegetarian diet can increase the risk for vitamin and mineral deficiencies, as well as omega-3 fatty acid deficiency, therefore supplementation may be necessary.
While vegetarian diets do not need to be high in carbohydrate, they do tend to be higher in carbohydrate than omnivorous diets, because meat tends to be replaced with starches. Therefore, if you are carbohydrate sensitive, you may tend to gain weight gain and lose control over appetite unless you are careful with carbohydrates.
To read about other popular diets, visit the Diets page.