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"Low-carbohydrate diets can lose more than 1.5 stones within three years," the Daily Telegraph said.
Researchers in the US conducted a test involving 164 people who had already lost weight on a 10-week diet during which all meals were given.
He assigned them to other 20-week diets to maintain weight loss.
During this phase, they received meals with different levels of carbohydrate – 60%, 40% or 20% of the total energy, representing high, medium or low carbohydrate diets.
Diets also differ in their fat content, while the low carbohydrate diet is supplemented with a fat content of 60%.
Weight loss and maintenance among the groups did not differ during the 20-week test.
But the researchers said the low carbohydrate group burned 209 more calories a day than the high carbohydrate group.
They predicted that at this rate, a typical 30-year-old man could theoretically lose up to 10 pounds for 3 years after the low carbohydrate diet. They made this assumption by analyzing the urine specimens of the participants.
The question of whether diets with a high carbohydrate or low carbohydrate content work better have been strongly challenged.
Recent studies have shown little difference in people's success in weight loss in 2 types of diet.
But these studies tend to be short-term. The difficulty is to measure the effects of a diet for many years, not weeks, in the real world where people choose their own food.
We also do not know how the combination of low-carb and high-fat diet would affect other health risks, such as heart disease.
Where does the story come from?
The study was conducted by researchers from the Boston Children's Hospital, Framingham State University, Arkansas University and Baylor Medical College.
It was funded by the Nutrition Science Initiative, the New Balance Foundation, the Multi-Voice Foundation and the Blue Blue Shield.
Published in the British Medical Journal and is free to read online.
One of the authors of the study has published several nutrition books that promote the concept of a low-carbohydrate diet.
The study accurately reported the results of energy expenditure.
However, the British media did not indicate that the study did not show long-term weight loss or maintenance or that the three diet groups were equally likely to have maintained their weight loss during the 10-week maintenance period.
What kind of research was this?
This was a randomized controlled trial, which is usually the best way to see if a treatment works.
But in this case the main results of the researchers concerned biochemical energy expenditure measures instead of actual weight loss or maintenance.
This means that the results suggesting weight loss are hypothetical, not really.
What was the survey involved?
Adults aged 18 to 65 at a university in the US were hired to take part in the weight loss study.
They all had a body mass index (BMI) of 25 or greater at the beginning of the study. They were paid to take part and had all the meals.
For 10 weeks, the 234 participants followed the same weight loss diet, designed to provide 60% of the estimated calorie needs, in order to lose 12% of body weight.
At the end of 10 weeks, 164 subjects (70%) had achieved the desired weight loss.
They were then randomly assigned to 1 of 3 weight maintenance diets for 20 weeks, in which calorie intake was adjusted to maintain their body weight stable.
Weight maintenance diets consist of:
- 60% carbohydrate, 20% fat, 20% protein (high carbohydrate content)
- 40% carbohydrates, 40% fat, 20% protein (moderate carbohydrates)
- 20% carbohydrates, 60% fat, 20% protein (low carbohydrate content)
The researchers gave the participants isotopically labeled water (where water was "labeled" with a substance) and compared urine samples before and after the diets to measure the participants' total energy expenditure.
This allowed them to compare average energy consumption in different diets for individuals with specific weights.
What were the main results?
The mean weight loss for the first part of the study was 9.6 kg.
Of those 164 who started weight maintenance, 2 stopped the study, leaving results from 162.
Of these, 120 remained within the 2kg goal of weight loss after the end (38 in the high carbohydrate group, 39 in the moderate carbohydrate group, 43 in the low carbohydrate group).
Using results from all 162 participants:
- the body weight was averaged below 1 kg during the maintenance phase and there was no significant difference in body weight change between the diet group
- energy consumption declined by 19kcal per day in the high carbohydrate group (95% confidence interval [CI], 104 to +66)
- the energy expenditure increased by 71kcal per day in the group of moderate carbohydrate groups (95% CI -12 to +155)
- energy expenditure increased by 190kcal per day in the low carbohydrate group (95% CI + 109 to +270)
- compared to the high carbohydrate group, the low carbohydrate group had a daily energy expenditure of 209 kcal per day
The ghrelin hormone, which says it increases hunger, reduces energy expenditure and promotes fat storage, was lower in people who had been on low carbohydrate diet.
How did the researchers interpret the results?
Researchers said the difference in energy expenditure, if continued for 3 years, would be translated into an estimated 10kg weight loss for a typical 30-year-old man weighing 1.78m and weighing 100kg, assuming there is no change in diet and average terms of activity.
"The composition of the diet seems to affect energy expenditure regardless of body weight," they said.
They added that a low carbohydrate diet "could help maintain weight loss beyond conventional focus on reducing energy intake and encouraging physical activity."
conclusion
Although the results of the study are theoretically interesting, they do not show any real, natural evidence of increased weight loss or improved weight maintenance for people on low carbohydrate diet instead of a high or moderate carbohydrate diet.
The study has several limitations. The authors say that the use of isotopically labeled water has been proven to be "the gold standard method for [measurement of total energy expenditure] to free living people ".
However, as the study does not include data on different weight loss from humans in 3 diets, we can not say if the measured difference in energy consumption results in differences in weight loss.
The study is also limited to how it translates into the real world. People in the study lost weight over a 10-week period, during which all their meals had been prepared, the calories and proportions of carbohydrates, fats and proteins being measured. This is not the way most people eat.
The study lasted only 20 weeks. We know that many people who lose weight during a diet measured in weeks or months will put weight back in 2 years.
This study provides interesting theoretical information on how the body can metabolize the diet of different food combinations.
It does not provide long-term real world research to show which diets work best on weight loss and maintenance in practice and whether there may be any relevant negative consequences.
Learn more about healthy weight loss with the NHS Weight Loss Plan.
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