Why is nutrition advice so confusing?
October 20, 2020
Nutrition experts seem to disagree on everything. Here’s why.
If you’ve spent any time reading about nutrition on the internet, it can feel like everyone has a different opinion on the best way to eat.
One person claims that meat is the best protein source, while another says a plant-based diet is all you need. Are carbs good or bad? And should you be eating a low or high fat diet?
When it seems like even the experts don’t agree on anything, how are you supposed to know what to eat?
To try and sort sound science from nutritional nonsense, we spoke to three of our experts, Professor Tim Spector - lead researcher for our PREDICT study - Professor Christopher Gardner, a leading nutritional scientist at Stanford University, and our resident nutritionist Dr. Haya Al Khatib.
Do nutrition experts really disagree about everything?
We wanted to find out how much disagreement on nutrition really exists.
We asked thirteen professors of nutrition to rank over a hundred foods according to how ‘healthy’ or ‘unhealthy’ they believed they were (see Figure 1). As it turns out, there are lots of areas of agreement.
“There was actually good agreement on the benefits of plant foods like fruits and vegetables, and the negative impact of very refined foods, which is in line with the majority of the evidence in the field of nutrition,” says Haya.
“It’s hard to find someone who disagrees with eating more fruit and vegetables,” confirms Tim, “But there will always be ‘experts’ with extreme views, especially on the internet, where people will suggest crazy things like eating soil. So you have to separate ‘internet science’ from actual science.”
But while experts generally agree on the extremes - refined sugar isn’t healthy, fresh vegetables are - things start to get a lot messier in the middle.
“While there was lots of agreement about foods that are obviously ‘good’ or ‘bad’ for us, there’s this huge battleground in the middle with foods that might or might not be good for us, including things like meat, cheese, yogurt and low-fat products,” says Tim.
“Meat and dairy, I think, are the biggest areas of contention,” agrees Christopher.
He highlights that it can be difficult to compare how healthy or unhealthy a food is without a specific context.
“Is dairy good or bad for you versus what? If you’re just trying to hydrate, then water can be a better choice than milk. But if you want calcium, milk could be better than water, but you could also look at fortified soymilk.”
How can we uncover the truth about healthy nutrition?
Studying nutrition is notoriously tricky. The perfect scientific study would randomly assign large groups of people to eat different carefully controlled diets over a long period of time, then follow their health outcomes. But while this might work for lab rats, it just isn’t going to work for humans.
Not only would this be unethical, it would be completely impractical. We all have our own tastes and preferences, not to mention allergies and intolerances. And we don’t just eat to fuel our bodies - we enjoy sharing food and drinks socially with family and friends.
“If we did a randomized control trial of meat-eating and non-meat-eating, for example, people might agree to do it for six weeks, but not for five years, yet that’s how long it takes to see real impacts on health,” says Tim.
As a result, nutritional studies tend to be observational, relying on seeing how people eat over a long time and how their health changes. But there are problems with this approach too.
“Usually, these studies are based on people reporting what they’ve eaten, and it’s not always that accurate,” says Haya.
As a result, the findings of this research are often conflicting and subject to interpretation.
“You get the results, and you draw a graph, and you think everybody would agree on how to interpret that, but they don’t,” says Christopher. “One person can look at the table and graph and say, I’m going to interpret that this way, while someone else interprets it another way.”
What’s more, while nutritional studies can give answers about how the people taking part in the research responded on average to different diets under particular circumstances, they won’t necessarily tell you how you, as a unique individual, will respond.
“There can be quite a lot of difference between people, particularly with these ‘middle foods,’” says Haya. “So one person might respond well to one of these foods, but another could benefit from staying away from it, but it all gets averaged out in the results.”
Fortunately, the latest science is starting to provide some answers.
Our research shows that everyone responds differently to food
Over the past few years, researchers are increasingly beginning to recognize that people respond differently to the same foods, and that this a crucial part of nutrition and health.
Our PREDICT studies have also shown how variable people's responses can be to the same foods. We found that even identical twins can have very different responses to the same foods, proving that genes only play a small role.
Importantly, we also found a wide range of dietary inflammation responses to the same foods in different people. Dietary inflammation is linked with increased risk for conditions such as heart disease, type 2 diabetes and obesity, so this finding helps to explain why there’s disagreement about the perfect ‘healthy diet’ and seemingly contradictory results from studies of diet and health.
What should I eat to be healthy?
Bringing all of this together, Christopher has some advice to help break through the confusing and conflicting advice about nutrition.
“We should all eat more vegetables, more whole foods, and less sugar, refined foods, and processed foods,” says Christopher. “That would solve about half our problems and health would improve dramatically. Then, we can start personalizing our diets based on what suits us best.”
This starts with understanding exactly how your body works. We have created a comprehensive at-home test kit that can help you better understand your unique biology - from your blood fat and glucose control to your gut microbiome composition. By using AI to compare your results to thousands of people who have participated in our clinical studies, we're able to reveal exactly how your unique body responds to hundreds of thousands of foods - no calorie counting needed. Ready to get your biology on your side?
- Nutritional science is a relatively new field of study, so we still have lots to learn
- When we asked nutritional experts to rank how healthy over 100 foods were, there were many areas of agreement
- Most experts agree on the benefits of plants, and the poor health effects of highly processed junk foods
- The disagreement comes when we look at foods like meat and dairy, which may or may not have health benefits
- Trials have shown conflicting results for these ‘middle ground’ foods
- Finding which foods are right for you comes down to knowing your unique biology
Find out more:
- Food fight erupts as top nutritionists gather to define healthy eating – STAT
- Why the heck can’t scientists agree on what is good to eat? – British Journal of Sports Medicine
- Why nutrition is so confusing – New York Times
- I asked 8 researchers why the science of nutrition is so messy. Here’s what they said. - Vox
- Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial – JAMA
- Human postprandial responses to food and potential for precision nutrition – Nature Medicine