Low carb diet: does carbohydrate reduction really help you lose weight?

This is probably the most controversial issue of the war on diet: what is the real importance of carbohydrates in weight loss?

On one side, a group of respected researchers; journalist Gary Taubes; and the Atkins, Zone, and Keto fans who pbadionately believe that if we could get past pasta, bagels and cookies, our weight struggles would be over.

On the other hand, equally reputable researchers and nutritionists have not adhered to low carbohydrate claims. Instead, they argue that most studies show that low carb diets are no better than other diets for weight loss.

It is a rich and lively debate. And Thursday morning, Dr. Oz jumped into the fray, appearing on the Today & # 39; hui show to highlight a new study showing that reducing carbohydrates can help people "lose weight, feel uncomfortable doing it, and maintain it," he said.

The study, led by researchers at Boston Children's Hospital, is published in the newspaper BMJ and is without doubt one of the most rigorous diet studies ever conducted. Although it did not show exactly what Dr. Oz had suggested, it's an important piece of evidence in this debate – and another reminder of the incredible difficulty of proving anything about nutrition.

The carbohydrate-insulin hypothesis

For this study, which cost $ 12 million, researchers sought to find out if it would be easier to maintain weight loss over 20 weeks with a low carb, moderate carbohydrate or high carbohydrate diet. But the question they were really testing is whether the type of calories we eat, not just the number of calories, matters for our weight.

Some nutrition and nutrition researchers argue that it is the amount that matters and that if we focus on reducing the number of calories, we will lose weight. Others think that the quality of calories matters enormously.

The main scientific model of the latter camp is the "Carbohydrate-Insulin Hypothesis," which Taubes, Harvard's Professor David Ludwig (author of the new journal), Robert Lustig of the University of California at San Francisco, have widely defended. This suggests that a high carbohydrate diet (especially refined cereals and sugars) leads to weight gain due to a specific mechanism: carbohydrates cause insulin in the body, thus forcing the body to retain fat and to suppress calories burned.

According to this hypothesis, to lose weight without taking it back, you must reduce the number of calories you consume in carbohydrates and replace them with fat calories. This is supposed to lower insulin levels, increase caloric expenditure and help fat to melt.

The new document is the best test of this hypothesis for "at-risk" participants – those who are not confined to a hospital or metabolic chamber for study purposes.

The new study of low carb, explained

Researchers, Boston Children's Hospital, Harvard Medical School and other universities, recruited 234 people and initially asked them to lose about 12% of their weight in nine to ten weeks.

They did it because we know that most people can lose weight with any type of diet, but the most difficult is to keep that weight. And the researchers wanted to know if a low-carb diet could help people suffering from this second difficult step, as suggested by the carbohydrate-insulin model, by having them burn extra calories.

Of the 234 people who started the study, 164 reached the goal of weight loss, which meant they were ready to move on to the next most important step in the study. # 39; test.

The remaining 164 participants in the study were then randomly badigned to a diet high in carbohydrate (60%), moderate in carbohydrate (40%) and low in carbohydrate (20%) and followed for 20 weeks at during which they have meals. Their diets were also carefully calibrated to make sure they maintained their new body weight.

After 20 weeks, the effects were quite remarkable: the less a person consumed carbohydrates, the more calories they burned – and, logically, the easier it would be to keep their weight. For example, those on a low carbohydrate diet burn over 200 extra calories each day, while those on a low carb diet burn about 100 extra calories per day, while those on a high carbohydrate diet do not burn do not burn them.

"This food study, the longest and longest to date, supports the carbohydrate-insulin model and credibly proves that not all calories are metabolically identical," said one of the authors. of the study, Harvard's Ludwig. "These results raise the possibility that a focus on carbohydrate restriction might work better for maintaining a long-term weight loss than calorie restriction."

Are these results applicable to most people?

Stanford researcher Christopher Gardner, who did not participate in the research, told me it was an "elegant study", the results of which deserve careful consideration. "It shows how long-term [a low-carb diet] can promote or prevent the maintenance of this weight loss. "

But Gardner also noted that the results may not yet be applicable to most people.

In most diet studies, where researchers do not eat all the calories, the low carb diet gives about the same performance as other diets in terms of weight loss. In other words, when you simply ask people to follow a low carbohydrate diet to lose weight, they lose about the same weight as people on a high carbohydrate diet. This is not a hard blow for the study, but for the fact that researchers do not yet know how to get people to follow a long-term diet, unless they feed them.

"If you prove that a mechanism works, but you can not get people to do it," Gardner added, "that's not going to help."

Importantly, other well-controlled tests of the hypothesis of low-carb insulin, in which people are placed in metabolic chambers, have not shown that diets low carbohydrate resulted in a significant increase in calories burned and weight loss.

But these studies are also problematic: they focused mainly on weight loss (not on weight maintenance) and they did not last as long as this one. It is therefore possible that the additional caloric expenditure does not really occur until after 10 weeks, as shown by the new study.

Another methodological question about the new study

Other researchers deeply invested in the debate over the low carbohydrate diet have raised another question about new research. It's pretty old-fashioned, but interesting, so support me.

Kevin Hall, an obesity researcher at the National Institutes of Health who studied low carb diets, said the researchers had used a technique called doubly labeled water to measure calories burned before and for the duration of the diet. study. This is to give the study participants a water sample containing (or "labeled") forms of the elements deuterium and oxygen-18. Because they are not normally found in the body, researchers can determine a person's metabolic rate – the amount of energy they burn each day – by following the rate at which they are expelled by urine.

Doubly labeled water is the method of choice for measuring energy expenditure in "free" subjects, that is, people who are not in a metabolic chamber. But there is a problem with the way it has been used in this document, Hall said.

When people just lose weight or their diet changes, doubly labeled water is less reliable. In their original study protocol – or their statement of intent before the end of the study – the researchers specified the following: they indicated that they would use the measure taken before the final weight loss phase as a baseline. People would then be stable in weight, and Hall said, "This is where the doubly labeled water has been validated."

But the researchers changed this end point because of an error, and instead makes their basis the beginning of the randomization of the diet – a change that they revealed in the study, to their credit.

The change, however, "has introduced noise to this extent," Hall said. Since people had already lost weight and their diet was changing, doubly labeled water could be a less reliable way of estimating energy expenditure. "And they do not report in the study what their data would look like if they used the measurement of weight loss before weight."

Hall took the pre-weight loss measures, which were reported in the study, and himself ran the numbers for a presentation at the recent Obesity Week conference. He found that the effect of caloric expenditure on the low-carbohydrate diet would have been much smaller if they had used this measure as a baseline: fewer than 100 additional calories per day of dietary group difference low carbohydrate and high carbohydrate content. may not be statistically significant.

"It's a tour de force [of science]Added Sam Klein, research scientist in metabolism and obesity at Washington University in St. Louis. But he shared Hall's concerns and felt that the study had produced results that seemed inconsistent with what we know about energy expenditure – probably because of the methodological problem raised by Hall. "Using this baseline before weight loss as a point of comparison reduces the size of the effect," Klein said.

Ludwig explained that these criticisms were based on a misunderstanding and that, as a result of a weight loss maintenance study, the use of the number of weight loss prior to the reference weight "would have contrary to this objective and introduced new forms of bias ".

"It's fair for any scientist to ask questions, rebadyze data and challenge interpretations," added Ludwig. "For the sake of maximum transparency, we have released the complete data set and the statistical code so that everyone can perform additional badyzes."

So should dieters stop eating pasta?

So back to the main question: should you avoid pasta if you want to maintain weight loss?

If you are confused now, you are right to be. Debates about the diet have become fierce and thorny. We all come to them with our prejudices, many interests are at stake and it is difficult to know what to believe. Nutrition studies – which are virtually impossible to achieve in order to reach irreproachable conclusions – are also easy targets: they are easy to criticize and interpret in different ways.

Apart from this new study, I have not found convincing evidence of the low carbohydrate diet. But maybe I'm too biased by my love for pasta, bread and cakes – and by personal experiences that have not allowed me to limit my carbohydrate intake – to fully enjoy a good time. life low in carbohydrates. (In fact, my long-term weight loss has coincided with the consumption of more carbohydrates than ever before.)

In my reporting years on diet and obesity, I know however that one thing is true: the same diets can have very different results depending on the people, and people can not lose weight if they follow an impossible diet. .

So, the best diet, as many wise people have already said, is probably the one you can stick to. If this sounds like a low carb diet, all the better. Maybe you can reap extra fruits by spending a lot of energy, baduming the results of the study resist. The researchers themselves have called for more studies, and replication will be particularly important since their results seem to diverge from the rest of the evidence base.

In both cases, Gardner said, "I have never seen anyone disagree on a less added sugar and a less refined grain. It's a huge part of the American diet. And you can not go wrong in adopting a diet with fewer nutrient-poor carbohydrates. "