Are plant based diets optimal?

There is a growing body of scientific evidence to support both the adequacy of plant based diets and its multiple health benefits. However, there are many who go further and argue that it is the most healthful diet there possibly is.

How far is that claim true?

Although sounding similar, it is one thing to assert nutritional adequacy of a diet or even its positive impact on health outcomes, but another matter altogether to claim that it is optimal in the strict sense of the term. The sheer volume and form of scientific evidence required to substantiate these two claims is vastly different.

When is a diet optimal?

Let’s first recognize that a given diet can be regarded optimal only if is better than practically any other alternative, including those that are minor deviations from it. In the case of a plant-based diet, the claim that it is optimal would require one to also establish that it is superior to an alternative that is identical in every way except for small addition of specific animal products — for example, half a serving of wild-caught fatty-fish or 2 free range eggs per week. In fact, we need to demonstrate that any animal based addition to an exclusive plant-based diet, in any form and in any frequency, is going to lead to worse outcomes in terms of health and well-being (all else being equal).

Scientific limitations

Now, there is no possible way one can meaningfully find support for such a hypothesis. Reliable conclusions based on scientific studies comparing diets can be reached only when there is a significant difference between them (unless of course that difference includes an important nutrient that is absent in one, or the small deviation is a known toxin, etc). If we are comparing two patterns of eating that are nearly identical, it is unlikely that science would be able to come to findings that are robust and reproducible.

And even if we could somehow carry out large population studies or trials comparing nearly identical diets, we would need a very large number of them to explore all combinations of minor deviations from a given diet to demonstrate that it is the optimal way of eating.

In practice, it is safe to say that cannot possibly hope to even prove that a diet is optimal because we cannot empirically test all of these minor variations.

And that is true for any diet, not just a plant-based one.

Furthermore, there are individual variations to consider. There are certain diets that work very well with certain sub-populations and less so with others. This is more likely to happen when we consider people having food allergies that forces them to restrict what they eat over and beyond what is already a restricted diet (such as a plant-based one). In these cases, getting all the necessary nutrients on the plant-based diet becomes challenging.

To be clear, well-planned plant based diets are indeed healthful. Indeed, across a range of health outcomes such as protection against diseases, reduced mortality, physiological parameters such as blood pressure, BMI or inflammatory markers, plant based diets have shown to confer several health benefits in individuals who have made a switch away from animal products.

However, it should be noted that while there is overwhelming evidence that a primarily plant-based diet is healthful for the vast majority of the population, there is almost zero evidence that exclusive plant based eating is optimal for even one individual.

Is it even important that plant-based diets are optimal?

There will always be individuals for whom following a strictly plant-based diet is going to be hard or that adherence to the diet doesn’t lead to the associated health benefits. These variations are true for any dietary or lifestyle interventions and there is no reason to believe that a vegan diet would be any different. In fact such variations are true even for efficacy of drugs in pharmacological interventions for various medical conditions.

When animal activists make the health argument for going vegan, the more accurate approach is to advocate for a diet that eliminates vast majority of animal foods. To claim that one can prevent/reverse Type 2 diabetes only on an exclusive plant-based diet simply doesn’t make sense.

There is yet another important but understated aspect to this. While we do often talk about making healthier eating or lifestyle choices, we rarely seek perfectly optimal decisions or more precisely, we are unwilling to make sacrifices required for optimal health. For example, let’s say that we somehow knew what is required for optimal health and that includes, among other things, specification of calorific intake everyday, the distribution of macros across those calories, the type of foods to be eaten raw, cooked or fermented, the exact number of times in a week to exercise and for how long, the number of hours to sleep and the need to stick to bedtime routine and limiting, if not eliminating alcohol altogether. It is impossible to see anyone aiming to achieve these targets precisely; we are often willing to operate away from that optimal zone because we value other things in life — freedom (from being obsessed), socializing, adventure, etc — besides optimal health parameters.

In much the same spirit, even if one could somehow argue that a plant based diet is optimal, that is rarely a clinching argument for people to stick to it because we do often make choices — and rightfully so — that are somewhat sub-optimal for a particular objective (health in this case) because we care about other things in life.

There is little sense — and no evidence to support — in claiming universal optimal diets even though, for a given individual, there might be a temptation to identify the one diet that will work perfect.