Large New Diet Study Has Just Disproved Many Pet Weight Loss Theories

Teach 600 people to eat more vegetables and less sugar throughout the year, and they will find themselves losing weight. There is nothing shocking about the DIETFITS study published today, but there is still a lot to learn about what doesn’t matter in diet.

Here are the main findings from a study published today in JAMA:

  • People on low-carb and low-fat diets have done much the same.
  • Both groups ended up eating fewer calories while not counting or reducing the number of calories.
  • People’s response to insulin (the amount of insulin their bodies release in response to a dose of sugar) did not predict which diet they would do best.
  • The three DNA variants that should have predicted your success … didn’t mean anything either.

The study itself is free of charge , but has a free breakdown of the study plan and results. This is the study other diet researchers have dreamed of. It is quite large – 300 people per group. This is a randomized controlled trial, which means people were told which diet they should follow. The researchers used more reliable methods than simply asking people what they ate. They also focused on getting solid answers to a few important questions they had identified ahead of time, leading to the results shown above, instead of asking a million questions and catching data errors.

Diets That Work

People on a low-fat diet have been advised to reduce their fat intake to 20 grams per day. This is what is found in four teaspoons of olive oil or three quarters of an avocado. McDonald’s Double Cheeseburger is far from the limit.

The low-carb dieters were also told to cut their carbs to 20 grams. This puts you in ketogenic territory, where your body changes its metabolism in order to supposedly become a fat burning machine. For comparison, half a cup of rice contains 22 grams of carbohydrates.

Both groups attended classes led by registered dietitians, at first one hour a week, and less frequently over the course of the year. For the first eight weeks, they were taught to cut their fat or carbohydrate intake (as the case may be) as low as possible. After that, they had to increase the amount of fat or carbohydrates a little to find out how much they can tolerate while still losing weight and enjoying their food. Here’s what they learned in class, according to a study report published last year:

Those assigned to the Low Fat Healthy Eating were asked to choose whole grains (for example, not whole grain flours), including steel oats, farro, barley, quinoa, brown rice, and wild rice. Healthy, low-fat participants were also asked to explore and consume a wide variety of legumes and legumes, fresh fruits, low-fat dairy products, and lean meats. Those assigned to the Healthy Low Carb Meal were asked to select high quality oils and fats, avocados, hard cheeses, nut butters, and nuts and seeds. During the titration phase [after the first 8 weeks] and throughout the remainder of the 12-month protocol, as the low-fat healthy group added small amounts of fat back to the diet, and the low-carb healthy group added small amounts of fat. the amount of carbohydrates back into the diet, they were instructed to do so with the same quality foods.

Given that high quality foods can be more expensive than lower quality foods of a similar type, the encouragement to choose quality was framed as a continuum rather than either / or (for example, for participants in a healthy low-fat diet, organic Wheat Berries were of the highest quality, followed by regular wheat berries, then whole grain breads made with minimal ingredients and no additives, then more traditional whole grain breads with many ingredients including additives, and finally refined white flour bread with many ingredients and additives was considered the lowest in the quality continuum). In other words, participants were encouraged to choose the highest quality products they could find, actually afford, and enjoy.

Most people have not actually reached the 20 grams goal. People on a low-carb diet averaged 96.6 grams of carbs by the end of eight weeks, and increased that amount to 132 grams by the end of the year. Low-fat dieters gained 42 grams of fat at the end of stage one and ate 57 grams per day by the end of the year.

But even though they didn’t quite achieve their goals, most people lost weight, no matter what group they were in. On average, both groups lost 12 to 13 pounds per year, but there were many individual differences! The guys at put together this graph showing the results. In each group, several people lost more than 55 pounds, and a significant proportion of the participants did not lose any weight at all or did not even gain up to 22 pounds.

What doesn’t matter

This study does not get us any closer to understanding why some people respond better to diet than others. And since each person has tried only one of the diets, we don’t know if people who gained weight on one diet would have done better on another.

The researchers hoped that genetics would discover the answer. Three genes, PPARG, ADRB2 and FABP2, have been identified in previous studies as possibly related to whether people are better off following a particular diet. So they looked at SNPs or gene variants known asrs1801282 ,rs1042714, andrs1799883 . If a person had versions of all three that were previously linked to the success of a low-fat diet and switched to a low-fat diet, they were thought to have genes that “matched” that diet. It’s the same with low-carb. Anyone whose genes were a mixture of genes low in fat and low in carbohydrates was considered inappropriate for their diet.

Unfortunately it didn’t work at all. The lead researcher told STAT , “We were so excited and thought it would work,” but after seeing the results, he had to admit, “We didn’t even get close.”

(Can I just tell my nerd from the bottom of my heart that it’s great that the negative research is still being published and debated, and the researchers aren’t trying to turn it into something it isn’t? It’s super good to know what’s not working especially in the age of questionable dietary coaching based on genetics.)

Insulin secretion also did not predict the success of a particular diet. When you eat food, especially carbohydrates, your pancreas releases insulin into your bloodstream as a signal for other cells to absorb the flow of nutrients. People with diabetes either don’t make enough insulin (type 1) or their fat and muscle cells don’t respond to insulin (type 2).

So they checked what happened to a person’s insulin levels 30 minutes after they drank a huge dose of sugar. Since type 2 diabetes is associated with obesity, the researchers wanted to test the theory that people who produce excess insulin would be better off on a low-carb diet that doesn’t produce as much insulin. But nothing came of this either.

What does this mean to me?

First, this study was conducted on a specific population of people, so we don’t know if the results apply to everyone. The participants lived in the Stanford Bay and San Francisco Bay areas in California. They were generally educated enough and usually had enough money to afford healthy food.

The study included only people with a BMI between 28 and 40 who were between 18 and 50 years old and did not take people with diabetes, heart disease, cancer, uncontrolled high blood pressure, or those who were pregnant or lactating. This leaves many people looking to lose weight and, in fact, many reasons why people want to lose weight (to control their heart disease or diabetes, or to lose weight as a child).

Both diets focused on eating more vegetables and less sugar, but this study does not prove if this is enough; you may also need to minimize nutrient intake. I would love to see a control group that did not aim to reduce carbohydrate or fat intake, but simply made a basic recommendation for a high quality diet.

And in the end, we really don’t know why some people lost 55 pounds while others gained more than 20. Researchers are planning more tests to find more answers. For now, however, we can assume that if you flip a coin, your chances of a low-fat diet are probably as good as a low-carb diet.

Updated 2/21/2018 7:00 AM to correct the title of the journal and the units of measure for some weight loss metrics (people lost up to 25 kilograms, not pounds – a big difference!)


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