Just Cutting Calories is Not the Key to Losing Weight
Just cutting calories is not the Key to losing weight, according to a new clinical trial. The Secret to shedding excess weight is eating a low-carb, high-fat diet, researchers found.
Among 164 adults in a weight-loss study, those placed on a low-carb, high-fat diet burned more daily calories, Vs those given high-carb meals. On average, their bodies used up 250 extra calories per day over 20 weeks. The carbs they ingested were strictly limited.
The researchers estimated that over 3 years, that would translate into an additional 20-lb weight loss for an average-height man.
“This study refutes the conventional thinking that it’s only calorie-cutting that matters,” said senior researcher Dr. David Ludwig. He is co-director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital.
Instead, he said, the source of those calories may make the difference in whether your metabolism “works with you or against you.”
According to Dr. Ludwig, the findings support a theory called the “carbohydrate-insulin model.”
The premise is that diets heavy in processed carbs send insulin levels soaring, which drives the body to use fewer calories, and instead store more of them as fat.
“Our study suggests that you’ll do better if you focus on reducing refined carbohydrates, rather than focusing on reducing calories alone,” Ludwig said.
He and his colleagues reported the findings online Nov. 14 in the BMJ.
Many studies over the years have attempted to answer the question of whether low-fat or low-carb is better for weight loss. Often, they concluded there is little difference.
But those studies, Dr. Ludwig said, have typically been behavioral studies where people may or may not stick with their diets.
So his team conducted a “feeding study” to carefully control what people ate.
First, 234 overweight and obese adults were recruited for a “run-in” phase, with the goal of losing about 12% of their weight over 10 weeks. Their diets were low-calorie and had moderate amounts of carbs.
Of that group, 164 lost enough weight and moved on to the next phase. They were randomly assigned to either a low-carb, moderate-carb or high-carb diet for 20 weeks.
People on the low-carb diet got 20% of their calories from carbs like vegetables, fruits and beans; a full 60% of their calories came from fat, including sources like meat, whole milk, cheese and nuts. The remaining 20% of calories came from protein.
The situation was flipped for people on the high-carb plan: 60% of calories from carbs and 20% from fat. The moderate plan divided the 2 nutrients equally, at 40/40.
After 20 weeks, the low-carb group appeared to be burning more calories, an average of 250 more per day, versus the high-carb group, and 111 more than the moderate-carb group.
The researchers did not look at the effects on any further weight loss. Instead, each person’s calorie intake was calibrated to maintain what they had already lost. The point, Dr. Ludwig explained, was to Zero in on the effects of the different diets on calorie burning.
According to Dr. Anastassia Amaro, an assistant professor of endocrinology and metabolism at the University of Pennsylvania, “The study design is very clever.”
Dr. Amaro, who was not involved in the research, said she already suggests that patients cut back on carbs when they are trying to lose weight.
These findings, she said, boosts her confidence in that advice.
However, Dr. Amaro said, the low-carb diet used in this study is not ready for a “direct translation” into the real world. For 1, she explained, it’s not clear whether it’s the lack of carbs that was Key.
“This is also a high-fat diet,” Dr. Amaro pointed out. “Is it the lack of carbs, the fat content, or both?”
The Big Q: What about the nutritional value of such a diet?
The Big A: Dr. Ludwig said it’s healthy allowing fruit, legumes and an “unlimited” amount of vegetables. What it does not have is grains and added sugar.
Dr. Ludwig agreed that more research is needed to show whether the approach is the best way to maintain weight loss. He and his colleagues recently started a new trial that will pit a very low-carb diet Vs 1 that is high-carb but low in sugar, and another that is high-carb/high-sugar.
The Big A: “That is a good question, but this study cannot answer it.”
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