Nutrition science was born in the early 1800s with the discovery of protein, carbohydrates, and fats. But long before that, humans knew a lot—strictly through trial and error—about food and health without actually understanding what the protective factors in foods were.
The first documented nutrition experiment was performed in 1747 by Dr. James Lind, a ship’s doctor with the British Royal Navy. At the time, being a sailor was a dangerous occupation, not just because of storms and piracy, but because as many as half of all sailors who set out on long voyages died from scurvy. Theorizing that it had something to do with the lack of fruits and vegetables on board, Lind fed different diets to a small group of sailors and noted that those who consumed lemons and limes didn’t get scurvy.
While the navy made good use of the information, ordering all British ships to carry limes, the reason that these foods were protective wasn’t known for another two hundred years when researchers discovered vitamin C. (And while Lind got all the credit for discovering the cure for scurvy, Chinese sailors had been growing greens on their ships to ward off scurvy since at least the fifth century.)
As early as 1916, well before the discovery of many vitamins, nutritionists were recommending intake of certain “protective foods.” The first RDAs were read over the radio to Americans in 1941 and have been updated and expanded a number of times since then.
Today, recommendations for individual nutrients are set by the Food and Nutrition Board (FNB) of the National Institute of Medicine. While these are official recommendations, the science behind them is sometimes still not entirely settled. In some cases, there isn’t enough research for anything more than an educated guess. And actual individual requirements are affected by lifestyle, overall diet, and genetics, which means that it’s impossible to pin down the exact nutrient requirements of any one person.
The recommendations are set at levels that are believed to meet the needs of the vast majority of Americans. Therefore, for any given nutrient, many Americans will need less than the recommended amount while others might need more. There can be exceptions, though. For example, many experts believe that current recommendations for vitamin D are far too low. And the debate about calcium recommendations is ongoing. We’re also starting to hear questions from world experts about protein requirements; some think that they may fall short of actual needs.1
Vegans And The RDAS
The dietary recommendations are aimed at omnivores and, in a few cases, nutrient needs might be higher for vegetarians and vegans. Protein requirements are believed to be slightly higher because plant protein isn’t digested quite as well as protein from animals. It’s a small difference and it’s easily satisfied with vegan diets as long as calorie needs are met and your diet includes high-protein plant foods. Zinc needs may also be higher, and it’s possible that some vegans have intakes that are less than optimal.
The situation for iron is a little more controversial. We’ll see that vegans have higher requirements but how much higher is a subject of some debate. We’ve included the FNB recommendations for iron in the chart below, but we don’t think that vegans should worry too much about getting this much iron.
Nutrient Intake Of Vegans: How Does It Compare To Recommendations?
There isn’t much available information about nutrient intakes of vegans, but a few studies show that vegans are likely to consume more of certain nutrients—vitamin C, thiamin, riboflavin, niacin, vitamin B6, folate, and sometimes iron—than omnivores.2 In contrast, many vegans have intakes of calcium and zinc that are lower than the recommendations. In the chart on pages 4 and 5, we’ve compared FNB recommendations to actual intakes of a group of British vegans.
Good Diets Are Good Advocacy
Whether you are already vegan or just starting to take steps in that direction, eliminating animal products from your lifestyle is an effective way to make a difference. It reduces animal suffering, removes your financial support for factory farming, and represents a stance against the use of animals. But in order to have the greatest impact possible, most of us who care about animals hope to influence others to go vegan as well.
Those who work for the meat, dairy, and egg industries would like to portray vegan diets as inadequate. So the last thing we want to do is give them any ammunition. Some vegans balk at the idea of taking vitamin B12 supplements, because they think it makes vegan diets appear inadequate. But taking a chance with nutrient deficiencies is the worst thing we can do for the image of vegan diets. For example, arguing that vegans have lower calcium needs than omnivores can cause some vegans to make poor choices for their bone health. Taking every precaution to make sure that we are healthy is one way to help others feel confident about going vegan.
Promoting veganism as a lifestyle that is practical, easy, and realistic is important, too. Time, convenience, and taste are primary factors in people’s food choices. That’s why overly restrictive diets can create the wrong kind of image for veganism. Current trends among some vegans to give up more and more foods—added fats, cooked foods, and gluten—are counterproductive, especially because these dietary restrictions have few health benefits for most people. It’s true that some people might have better success with weight control when they eat very little fat, but research suggests that diets containing small amounts of added fats or higher-fat foods can be even more beneficial for long-term weight control. And we’ll look at why a little bit of unsaturated fat in the diet, especially monounsaturated fat, can be good for controlling and preventing chronic diseases.
Likewise, the idea behind a raw foods diet is based on a few scientific principles that are shaky at best. There is really no good evidence to suggest that eating all raw food is any better for you than eating a mix of raw and cooked whole plant foods. In fact, some of the beneficial compounds in foods, such as lycopene (an antioxidant in tomatoes that protects against prostate cancer), are available only when foods are cooked. The vitamin A precursor beta-carotene is more readily available from cooked foods as well and is also better absorbed in the presence of some fat. A raw foods diet can be helpful for weight control, since it has a lower caloric density, but this also means that it isn’t appropriate for children.
A gluten-free diet is an absolute necessity for those who have celiac disease, a permanent intolerance to gluten. But this autoimmune disease affects only 1 percent of the population. That means that most vegans have no reason to eliminate gluten from their diets. In fact, some research suggests that gluten-free diets are associated with reductions in levels of beneficial gut bacteria and increased levels of harmful microbes. For those who don’t have celiac disease, it may be beneficial to include some gluten in their diet. (Of course, those who have allergies, including non-celiac wheat allergy, need to adjust their diets accordingly.)
Promoting these additional restrictions that have no known health advantage for most people doesn’t do anything to help animals or promote vegan diets. To the contrary, it creates an image of vegan diets that makes them look more difficult and less appealing. If we want others to follow our lead in adopting more compassionate food choices, it makes sense to avoid unnecessary restrictions and make vegan diets as accessible as possible.
The nutrition recommendations in this article, which are based on solid, current science, are aimed at making your vegan diet healthful and realistic. You’ll see that it’s easy to meet nutrient needs by eating a variety of cooked and raw plant foods, and it’s also reasonable to plan some family meals using convenience products without compromising your health.
Supplements In Vegan Diets
With the exception of vitamin B12, it’s possible to get all of the vitamins and minerals you need from plant foods. Depending on individual circumstances, though, vitamin supplements can provide an important way to meet nutrient needs, especially for vitamin D, iodine, calcium, and DHA.
While it’s possible to purchase vitamin supplements that are food concentrates, many are synthetic—that is, they are synthesized in a laboratory. As long as they are well-digested, synthetic vitamins and minerals will do their job. In fact, in some cases they are a better source of nutrition than the food concentrates. For example, some “natural” vitamin B12 supplements are produced by companies that have not used proper testing standards and therefore, the B12 is not a reliable source of that nutrient.
The United States Pharmacopeia (USP) verifies the quality, purity, and potency of dietary supplements for companies that take part in their certification program. Supplements that display the “Dietary Supplement USP Verified” mark on labels have been tested to verify that they dissolve properly. (Vitamin and mineral supplements that don’t carry the USP symbol may still be of high quality; it just means they haven’t been certified.)
The supplements we recommend are for nutrients that can be low enough in vegan diets to lead to a deficiency. While a multivitamin can provide a number of these nutrients all at once, taking them as separate supplements will allow you to take only the supplements you need. A few things to keep in mind regarding supplements: First, most of us have sufficient stomach acid to dissolve supplements for thorough digestion. But if you have reason to believe that your stomach acid isn’t strong, it’s a good idea to crush or chew vitamin and mineral supplements. Also, supplements sometimes require a bit of attention to balance. For example, high doses of zinc can inhibit copper absorption. Taking 50 milligrams of zinc per day (the RDA is 8 to 11 milligrams) can cause a copper deficiency in just a few short weeks. This is one reason to rely on a well-balanced diet to provide enough nutrients and use supplements just to make up for any shortfall.
Keeping Nutrition Simple
Humans require more than forty essential nutrients. Most people know that they need nutrients like vitamin C, protein, and calcium. But they may never have heard of the B vitamin biotin or the mineral vanadium and have no idea that they need to consume foods that provide these nutrients. And it’s definitely not something you need to worry about. Most nutrients are so readily available in all different types of diets that we don’t need to think about how to get them.
In this article, we’re going to focus on just nine nutrients—protein, calcium, iron, zinc, iodine, alpha-linolenic acid, and vitamins B12, A, and D. We’ll briefly mention a handful of others and talk about DHA, an omega-3 fat that doesn’t have essential nutrient status (meaning that, while a growing body of evidence suggests that it’s important, it hasn’t been established as a dietary essential). These are the nutrients that are of special interest to vegans and are the center of vegan nutrition. Getting enough of them isn’t difficult. You just have to know how to do it.
Nutrient Recommendations: Some Terminology
Depending on the available research, determining precise needs is easier for some nutrients than for others. If researchers don’t have enough data, or the findings are conflicting, it can be difficult to reach conclusions about optimal intakes. Therefore, current recommendations fall into several different categories, which are collectively known as the DRI (Dietary Reference Intakes):
Recommended Dietary Allowance (RDA): The amount of a nutrient that is believed to be sufficient to meet the needs of 97 to 98 percent of the population. It varies for different age groups and between men and women.
Adequate Intake (AI): When there isn’t enough data to establish an RDA, the Institute of Medicine sets an AI, which is based on both studies and observations of what healthy populations consume. The recommendation for calcium, for example, is an AI because the data regarding calcium needs is conflicting.
Tolerable Upper Intake Level (UL): This is the maximum daily intake of a nutrient that is likely to be safe. Some nutrients can be extremely toxic at higher than normal levels, although excessive intakes are almost always associated with supplements.
Daily Values (DV): These are values used strictly for food labeling purposes and they are based on much older RDAs. The amounts of vitamins and minerals in a food are listed as a percent of the DV. For example, the DV for calcium is 1000 milligrams, so if a food contains 10 percent of the DV for calcium per serving, it provides 100 milligrams of calcium. The problem is that without knowing what the DV is for a specific nutrient— and the food label doesn’t tell you—it’s hard to know exactly what these numbers mean. As we discuss the nutrients that are especially relevant to vegans in the next articles, we’ll give you the information you need to decipher food labels.
Understanding Nutrition Research
The amount of nutrition information in the media and on the Internet is staggering. Much of it is conflicting and often studies looking at the same question come up with completely different answers.
In fact, for essentially all heavily researched areas, you can build a case for just about anything by picking and choosing the studies that support your point. Some advocates do this to make vegan diets look more beneficial. And some vegan detractors pick a completely different set of studies to make vegan diets look bad.
The key to understanding nutrition research is to look at the entire body of evidence and see what most studies say. Rarely can a single study provide a definitive answer to a question. There are always inconsistencies and there are always study flaws. In addition, different types of studies carry different weight. So the strengths and weaknesses of certain types of studies have to be balanced against the strengths and weaknesses of others.
Types Of Studies
These types of studies don’t provide conclusive evidence but are conducted primarily to determine if further research is warranted.
- Neither in vitro (studies conducted in test tubes or cell culture often using single cells) nor animal studies can serve as the basis for conclusions about diet and disease. Aside from any ethical considerations and despite their widespread use, findings about nutrition from animal studies often can’t predict what is going to happen in humans.
- A case study is an observation about one or perhaps several patient histories and their treatment and disease outcomes that is published in a scientific journal. Often these types of reports can be used as a basis for hypothesis generation, but they don’t provide definitive answers. In contrast, if a report isn’t published in a peer-reviewed journal, it is merely an anecdote and has little or no value in contributing to nutrition knowledge. A great deal of nutrition information on the Internet —including books by doctors and other health professionals—is based on anecdotes rather than actual science.
- • Ecological (also called correlational) studies compare food habits and disease rates among different groups of people. One ecological study that is familiar to many vegans looked at rates of hip fracture and protein consumption in different countries. The results showed that as protein intake increases, so does the rate of hip fracture. But contrary to popular opinion, that study didn’t show that high protein intake causes weak bones. It did set the stage for clinical studies on how protein might impact calcium metabolism.
Another type of ecological study is the migration study, which looks at what happens to the health of people when they relocate and acquire the food and lifestyle habits of their adopted homeland. These kinds of studies can help show whether risk for certain diseases is related more to genetics or lifestyle.
Ecological studies are riddled with problems because there are many factors that affect health outcomes and these can’t be completely controlled for in the analysis of the data. Additionally, individual food intakes can only be roughly estimated.
Better Evidence: Epidemiologic Research
Epidemiologic studies can establish that two factors occur together but not that one causes the other. They are prone to confounding variables, which means that there might be unidentified issues that cause two factors to be associated. For example, if researchers find out that people with low fruit intakes are more likely to get cancer, it seems logical that fruit is protective against this disease. But what if those who don’t eat fruit also don’t exercise? It’s difficult to establish whether it is lack of fruit or lack of exercise or a combination of both that raises the risk.
Ecological studies, discussed above, are the weakest type of epidemiological studies. The following three types of epidemiology provide stronger evidence.
- Retrospective studies compare past eating habits between people with and without a particular disease. For example, if people with heart disease are more likely to have eaten a diet high in saturated fat, we might conclude that saturated fat has something to do with heart disease. The main drawback of these studies for nutrition research is that people’s memories of their previous diet can be faulty, especially if it has changed over the years.
- Cross-sectional studies compare eating habits and disease rates in groups of people at one moment in time. One problem is that people who have recently become ill may have recently changed their diet.
- Prospective (also called cohort) studies follow large numbers of people who are (usually) healthy when the study begins. As the population is followed, eating patterns of those who eventually get a disease are compared to those who do not. These studies require a lot of subjects—numbering in the tens of thousands—and take place over a long period of time, but they carry the most weight among epidemiologists
Best Evidence: Clinical Trials
The randomized controlled trial (RCT) is the gold standard in nutrition research. It’s the most credible type of study because it randomly assigns people to different groups and then controls what they eat. Ideally, the study is double-blinded; that is, the subjects don’t know whether they are in the test group or the control group. And when the researchers collect the data, they don’t know which group it came from until all the data has been collected and analyzed. The effects of different supplements or foods on disease markers, like cholesterol or bone density, can be studied this way. These studies can be very powerful, and ideally, everything we want to know about nutrition would be tested through RCTs. Unfortunately, they are expensive and complex, which is why they are often smaller in size and shorter in duration than is ideal.
A Word about Statistics
Statistical analyses are always performed to eliminate the probability that different outcomes occurred by random chance. Generally, a finding is statistically significant if there is less than a 5 percent chance that it occurred by chance. When studies are small in size, it becomes difficult to show statistical significance. Even if there appears to be an effect of a treatment or differences between groups, if the differences and treatment are not statistically significant, scientists conclude that there was no effect.
One way to make good use of the data from smaller studies is to do a meta-analysis. This is a statistical analysis of a large number of studies for the purpose of integrating the findings. It is often done to compensate for the small size of individual studies.
Scientific journals make sure that studies are credible and worth publishing by having them reviewed by other researchers qualified to do so. The reviewers can recommend that the study be published or not, based on what they think of the study design and other factors.
Who Paid for the Study?
Most nutrition research is funded by the government, but some is paid for by industry. It probably doesn’t matter as much as you might think.
The results are what they are and the sponsoring party can’t change them. The only real advantage is that they get a peek at the data before it is published; that way their PR department can be ready to issue a press release.
In conclusion, we can make educated statements about vegan nutrition only by looking at what most of the studies say (rather than drawing conclusions from individual studies) and by focusing on the studies that are likely to yield the most reliable information. It’s also important that studies are published in peer-reviewed journals.