I get the questions all the time on social media: Which diet is best? Should I be vegan or keto? If you want a quick way to get into a heated argument, just get online and start making a case for a specific diet. But I’m not just avoiding controversy—I truly believe there’s no right answer to those questions.
Food and Nutrition are Complex
Nutritional philosophy is notoriously controversial, with diet wars raging in every corner and competing claims coming at you daily. One reason for this is that nutrition research is challenging to do. It’s hard to control variables and confounding factors. Often, there isn’t an immediate health impact of a dietary intervention, so these studies can take a long time, making them more expensive. Getting participants to adhere to interventions is challenging, as is getting accurate recall of when and how much they ate—the basis for longitudinal studies. We like to study the impact of foods in isolation, but in the real world, foods are almost always consumed in combination, and that combination (or different cooking methods) can change the bioavailability of parts of that food.
On top of that, food processing can affect the bioactivity of food. For instance, chopping raw garlic activates an enzyme called alliinase, which converts garlic’s alliin compound to its active form, allicin. Allicin has been shown to have potent antimicrobial properties in the lab and in humans, but if you study raw, unchopped garlic, you may not see this effect.
All of these things make it difficult to know what’s best to eat, even for the researchers doing the studies. What hope do you have to find the one right way to eat?
Here’s an example of the complexity that makes research and dietary recommendations challenging. Omega-3s can come from various sources: fish, meat, eggs, nuts, seeds, algae. But there are different forms of omega-3s, and typically, plant sources contain the “upstream” omega-3s (like alpha-linoleic acid, ALA) that need to be converted through multiple chemical reactions (enzymes) to the downstream form that is most active (EPA and DHA) for making up cell membranes, and promoting anti-inflammatory reactions. Eating fish or other omega-3-containing animal products will give you straight EPA and DHA, but if you’re eating plant-based sources, you are mostly getting upstream ALA and have to convert it.
Here’s the catch: Converting ALA to EPA requires the function of three sequential enzymes, and these enzymes require regulating nutrient cofactors, including vitamins B3, B6, and C, zinc, and magnesium. So you need to eat targeted, diverse foods to get the vitamin and micronutrient levels that make this conversion possible. Eating plant sources of omega-3s but being deficient in nutrient cofactors could mean you’re missing most of the omega-3 benefits.
In other words, there’s no correct answer to “how do you get the omega-3s you need?” It’s amazing the body can be so flexible and simultaneously frustrating if you’re trying to deliver nutrition advice in a quick one-liner.
But the Basic Principles are Simple
Seen another way, food can also be simple.
First, nutrition research sometimes gets bogged down in too many details. While the molecular biology of food is critical to understand, the epidemiology of food can also help guide us. We also know that people who eat ultra-processed foods, too many omega-6 fats, and excess sugar tend to have higher rates of chronic disease and early death. We know that including omega-3 fats, adequate micronutrients and phytonutrients, and antioxidant-rich foods supports longevity.
Looking at nutrition through that larger lens helps us appreciate the overlap between all of the major dietary ideologies, and this overlap is where some essential nutritional truths emerge.
What could whole-food, plant-based eaters and carnivore enthusiasts possibly have in common? One group eats only plants, and the other only eats meat. But in fact, these dietary ideologies share traits:
- Both focus on the nutrient density of food, striving to get as many nutrients as possible from what they eat.
- Both eschew processed foods, and in particular, abstain from processed grains, sugar, food additives, and seed or vegetable oils.
- Both take a thoughtful approach to food sources and sustainability, with an appreciation of the importance of soil health.
When we follow those three principles, we can create many diets that feed our body the information it needs to thrive.
So my answer to “Which diet is best?” is simple: Humans around the world have had varied diets for millennia. Focusing on dietary ideology is less important than focusing on principles. And the key focus of any dietary strategy should be ensuring what you are eating has the necessary components to support optimal cellular biology.
The good thing is that several different dietary approaches—when thoughtfully crafted—can give you these components.
— Dr. Casey
Further reading: The Levels Dietary Philosophy