In Romania, they say that everyone is an expert in football and politics. But I believe it is more appropriate to say that everyone is an expert in food—or so they think. Except for a small minority, most of us have quite strong opinions about what we eat.
Even children of one or two years old have formed an opinion, although it often differs significantly from that of the adults who take care of them. And while some keep their opinions to themselves, others, for well-intentioned reasons, share them freely and try to convince others of their truth.
What do diets and mushrooms after the rain have in common?
The internet is full of posts about diets that are intended to be informative or educational. People frequently give their opinion on social media, most of the time starting with personal experience (“I’ve been eating this way for seven years and I feel great!”) or with some more or less scientific arguments (“Why else do we have canine teeth other than to eat meat?”).
On some obscure website, you might discover that it has been shown that people who exclude meat from their diet suffer from heart disease much more frequently than those who eat meat. On another site you learn that, on the contrary, vegetarians have lower cholesterol levels than meat eaters, and heart disease is not as prevalent among vegetarians.
Not to mention the countless weight loss “diets” or “regimes” based on all kinds of contradictory ideas: low-carb, low-fat, raw, very low-calorie diets (“100 calorie diet”, “400 calorie fix diet”, “1200 calorie diet”), high-protein, low-glycemic, ketogenic, gluten-free, for rapid weight loss, meat replacement, three-apples-a-day, three-hour diet, three-day diet, four-hour diet, four-day diet, Atkins diet, Bernstein diet, and more.
People eat very diversely, and it probably rarely (if ever) happens that two people’s diets and food preferences coincide completely. However, we can identify certain diets or food regimes that have common characteristics, for which certain terms are used: omnivorous diet, lacto-ovo-vegetarian, lacto-vegetarian, pescetarian, partially vegetarian, strictly vegetarian or vegan, fruitarian, macrobiotic, and so on.
The most common and important types of diet that arouse certain controversies among their supporters are the omnivorous diet, the lacto-ovo-vegetarian and the strictly vegetarian, or vegan. Are any of these three diets superior to the others? Or, conversely, are any of them harmful to health? What are the advantages and possible disadvantages of each? What do we know from the scientific studies published so far and what do we not know yet?
Why do expert opinions differ?
To start, it should be noted that even experts have differences of opinion regarding the interpretation of certain studies in the field of clinical nutrition. Such differences are explained, primarily, by the limitations of the current research methodology on the effects of food on human health.
There are several types of studies used to establish correlations between the consumption of certain foods and certain chronic diseases (cancer, diabetes, cardiovascular diseases, etc.). They are not simple unambiguous experiments or simple mathematical demonstrations but are affected by certain limitations and margins of error, so it is important to understand the limitations of the respective studies.
The first category of studies is based on international or intranational (interregional) comparisons; these studies verify the existence of a correlation between the estimated national or regional consumption of certain nutrients or foods and the incidence of certain diseases or the mortality rate caused by certain diseases in two or more distinct populations. For example, the incidence of cancer or cardiovascular diseases can be compared between countries that predominantly embrace a Mediterranean diet and those with a Western diet.
International and intranational studies have numerous limitations that make it difficult to interpret the results. For one, the estimation of nutrient and food intake can be affected by large errors. Another is that there are differences in the detection (diagnosis) of certain diseases and in the administrative reporting systems between different countries. For example, if the cancer reporting system in a country is deficient and only a part of the total cancer cases is reported it can create a false interpretation of a lower incidence of this condition, attributed to either higher or lower consumption of certain foods, although in reality, it is an erroneous reporting.
Migrant studies estimate the incidence or rates of mortality or morbidity in certain populations that migrate from one place to another. For example, studies have been conducted on Japanese populations in Japan and, comparatively, on Japanese populations in the US. These studies ensure the same genetic background of the subjects, but do not control the rest of the environmental factors (population density may be different in an area of Japan from a state in the centre of the United States).
The “case-control” studies compare the consumption of certain foods in patients who have a certain disease and in subjects who do not have the disease but who otherwise share similar characteristics (same sex, age, race, city or region of residence, etc.). Although such a study design ensures better control of sources of error, they are not completely eliminated: control subjects may not have been chosen to be similar enough; if the disease develops slowly but the patients are asked what foods they are eating at the time of the study, the risk factor may have been related to a past diet (and if the patients are asked about their past diet, they may not correctly recall what and how much they consumed); participation rates in such studies are often low, which affects the representativeness of the subjects and the generalisability of the conclusions.
Finally, prospective cohort studies (longitudinal cohort studies) involve the evaluation of the diets of a very large number of healthy individuals (this very large group of subjects is known in epidemiology as a “cohort”). These people are then followed over a long period until a sufficiently large number develop the condition of interest (cancer, diabetes, etc.).
When a sufficiently large number of cases have been detected, a comparison is made between the diet of the people who developed the disease and of those who did not. Prospective cohort studies have fewer methodological limitations than those previously mentioned, but they are still affected by errors: these studies require long periods; many subjects can be “lost” before it is known whether they developed the disease or remained healthy; the diet can change between the initial and the final time.
Due to these methodological limitations, the results of certain studies are often viewed with scepticism by some experts and attributed to chance (especially since each expert interpreting the data will naturally be influenced by their own biases). Still, we should note that when, in an (almost) systematic way, a certain effect (positive or negative) is observed for a certain diet, the probability that that effect is not due to pure chance is much higher.
In other words, a result obtained in a single study should be taken with a grain of salt, but ten similar results in ten different studies suggest that there is more to it than mere chance. It’s similar to someone playing the lottery ten times and winning each time; most of us would suspect that it is not a coincidence but they have a secret to winning.
Well-planned vegetarian or vegan diets can be just as healthy as an omnivorous diet
An omnivorous diet—in which, in addition to plant foods, animal foods and primarily meat are also consumed—is generally considered a “normal” diet. Especially in Western societies (but not only in the West), the majority of the population has an omnivorous diet. For example, in the United States, a 2006 statistic showed that 97.7% of the population has an omnivorous diet (including people for whom the only animal product eaten is fish).
In Canada, statistics available from 2003 showed that around 96% of the population are omnivores. In Europe, the highest percentage of omnivores are found in Italy and Germany (about 90% and 91%, respectively).
Evidently, vegetarians are a minority in these geographical areas. For this reason, many assume that a meat-centred diet is healthy and that a lacto-ovo-vegetarian or a vegan diet is deficient. However, in light of current scientific data, the two minority diets can be at least as healthy if carefully planned.
An educational resource from the British Dietetic Association supports the idea that a well-planned vegan diet can “support healthy living in people of all ages.” This is also the position of the American Dietetic Association and Dietitians of Canada, according to which “appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases. These diets are appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood, and for athletes.”
An article published on the EUFIC (European Food Information Council) website, contains a similar conclusion: “If executed well, vegetarian diets can be a viable alternative, yet a higher fruit and especially vegetable intake remains an important goal for vegetarians and meat eaters alike.”
EUFIC is a “non-profit organisation which provides science-based information on food safety and quality and health and nutrition to the media, health and nutrition professionals, educators and opinion leaders, in a way that promotes consumer understanding.” However, in Europe, there is no position paper adopted by the European Federation of the Associations of Dietitians regarding vegetarian diets.
The expressions “appropriately planned” and the like are worth noting, as vegetarian diets that do not meet this condition may not be healthy and nutritionally adequate. However, it should not be overlooked that an omnivorous diet must also be “appropriately planned,” since omnivorous diets are not without risks if they are not judiciously constructed.
Robert Ancuceanu is a doctoral professor at the Faculty of Pharmacy within the “Carol Davila” University of Medicine and Pharmacy in Bucharest, Romania.