A Big New Diet Study Just Disproved Several Theories on Weight Loss

The  DIETFITS  study published today isn’t super surprising, get 600 people to eat more vegetables and less added sugar for a year and they’ll lose weight. What is interesting in the study are the takeaways regarding what doesn’t matter when dieting.

The study, published today in  JAMA Nutrition  provides a few key takeaways:

  • Low-carb and low-fat dieters achieved essentially identical results
  • Both groups ate fewer calories despite not being told to count or reduce calories
  • Insulin response did not predict which diet would elicit the best response in each individual
  • DNA variations believed to predict success in the respective diets meant nothing

The study was big – 300 people per group and was a randomized controlled trial. Low-fat dieters were told to reduce their fat intake to 20 grams per day and  low-carb dieters were told to reduce their carbs to 20 grams, as well. That puts you into ketogenic territory.

Both groups went to classes taught by registered dietitians were they were taught to get their intake of fat or carbs as low as possible. They were then expected to slightly increase their fat or carb intake to find out how much they could tolerate while still losing weight. Here’s a breakdown on the class:

Those assigned to Healthy Low-Fat were instructed to choose whole-grain foods (e.g., rather than whole wheat flour products), including steel cut oats, farro, barley, quinoa, brown rice, and wild rice. Healthy Low-Fat participants were also encouraged to explore and consume a wide range of legumes and beans, fresh fruit, low-fat dairy products, and lean meats. Those assigned to Healthy Low-Carb were instructed to choose high quality oils and fats, avocados, hard cheeses, nut butters, and nuts & seeds. During the Titrate phase [after the initial 8 weeks], and throughout the remainder of the 12-month protocol, as the Healthy Low-Fat group added small amounts of fat back to the diet, and as the Healthy Low-Carb group added small amounts of carbohydrate back to the diet, they were instructed to do so with these same quality foods.

Given that high quality foods can be more expensive than foods that are similar in type but lower in quality, the encouragement to choose quality was framed as a continuum as opposed to an either/or (e.g., for the Healthy Low-Fat participants, organic wheat berries was at the highest level of quality, followed by conventional wheat berries, then whole wheat bread made with a minimal number of ingredients and no additives, then a more conventional whole wheat bread with many ingredients including additives, and, finally, refined white flour bread with many ingredients and additives was considered the lowest end of the quality continuum). In other words, participants were encouraged to choose the highest quality foods that they could reasonably find, realistically afford, and enjoy.

Participants lived in the Stanford and San Francisco Bay areas of California and they tended to be fairly well educated and were well off enough to easily afford healthy food. The study only included people with a BMI between 28 and 40, who were between the ages of 18 and 50. The study did not accept people who had diabetes, heart disease, cancer, uncontrolled high blood pressure, or who were pregnant or lactating

Both diets involved a focus on eating lots of veggies and less sugar, but both groups worked to minimize a nutrient (carbs or fat). It would have been interesting to see a control group that wasn’t given a goal to lower carbs or fat, but rather was just held to the high quality diet advice.

It’s the kind of result that begs the question “what do all these diets have in common?” My answer would be: they make you pay attention to what you’re eating. And when you pay attention to what you eat, you eat better. There’s no trick to losing weight, it’s all about energy balance.