Why One-Size-Fits-All Diets Don’t Always Work

Maybe you follow a strict Mediterranean diet or keto or Paleo, and find you’re getting nowhere in terms of your body composition goals even after a few months — yet your friend gives it a try and within a few weeks, sees major results. What are you doing wrong?

A new study indicates it’s not your approach or even the fault of a few “cheat days.” It’s how your body is reacting to the food.

In the largest nutrition research of its kind, led by an international team of scientists and researchers found individual responses to the same foods are unique, even between identical twins.

The recent study looked at more than 1,000 pairs of identical twins, who were studied for two weeks of blood sugar monitoring, insulin response and body fat levels. Although that amount of time is considered short in the research world, it was still long enough to find participants had a wide variation in responses to the exact same meals.

For example, some participants had rapid and prolonged increases in blood sugar and insulin, which could lead to weight gain and diabetes. But an identical twin may not have had that reaction at all, even after eating the same food.

The focus on identical twins is very helpful, since it eliminates some of the genetic and environmental differences that might otherwise exist in this kind of study. It allowed researchers to look at personal differences in metabolism instead. What they found was factors like gut microbiome, meal timing and exercise play a major role when it comes to how an individual processes food.

“It is reassuring that our genetic makeup only partially explains how our bodies respond to food,” says researcher Dr. Andrew Chan, a professor of medicine at Harvard Medical School. “This underscores that our metabolism is not fixed; we have the power to change it. One exciting avenue is to tailor our diets to the bacteria in our gut that helps us metabolize nutrients.”

Nutrition experts often advise against trendy diets that carve out whole food groups or achieve weight loss through severe calorie restriction. But what about a tried-and-true eating plan like the Mediterranean diet, which is considered the gold standard of nutrition at this point?

A recent study suggests even that approach — rife with vegetables, whole grains, fish, beans and nuts and red wine — may not work for everyone. Data from nearly 300 controlled trials on nutritional supplements and recommended diets, including the Mediterranean, found the eating style resulted in only modest improvements in cardiovascular risk.

“There’s simply not enough convincing evidence to say this is how everyone should be eating,” says Dr. Safi Khan, the study’s lead author and an assistant professor atWest Virginia University. “The fact is that there’s no single magic diet that’s good for everyone.”

Where do you go now that you know nutrition needs to be individualized and that even a generally accepted strategy like the Mediterranean diet may not be your ideal plan?

Food tracking using an app like MyFitnessPal can be very helpful, according to Mike Israetel, PhD, chief sport scientist and co-founder of Renaissance Periodization, as well as a nutrition consultant for the U.S. Olympic weightlifting team. That gives you a starting point for making adjustments to your macros — protein, fat and carbs — that may be more appropriate for your goals.

Focusing on foods that are nutrient dense and contain more protein and healthy fats is also a good starting point, advises Joyce Faraj, PhD, a nutritionist at Mountainside Treatment Center.The main message here is that adjustments, even when you seem to have found the eating plan that works best for you, will likely be a regular part of your goal-reaching strategy.

For example, your metabolism often shifts as you lose weight, so you’ll have to change your macros over time, says Israetel. That may be frustrating if you’re looking for an easy, dependable nutrition style that feels like a “set it and forget it” way of eating. But for consistent results that keep your body fueled, re-adjustment based on how your body reacts is likely the better way to go.