This is still the moment. It's time to revise dietary recommendations for Americans, which happens every five years. This time around, these revisions will come under the blame that over the past 40 years, the guidelines have not only helped Americans eat better, but they have also contributed to our obesity problem.
Here is the theory. By suggesting that Americans limit their consumption of fat, the guidelines have led to a reduction in fat content and an increase in carbohydrates. This change was at least partly responsible for the rise in obesity.
Let's see what the government told people to eat and what they actually ate. The first version of the guidelines in 1980 recommended limiting fat to 30% of calories. This recommendation was maintained until 2005, when the limit was increased from 20% to 35%.
Has anyone listened? I asked Mal Nesheim, professor of nutrition emeritus at Cornell and chairman of the Advisory Committee of Dietary Guidelines of 1990. "It's hard to say," he told me. "The average fat consumption has not decreased much." He is right. From 1980 to 1997, fats increased from 41.3% to 37.3% of calories (although actual fat consumption increased, carbohydrate consumption increased further), and then began to recover.
It's a small drop, but it could easily mean that some people have significantly reduced their fat consumption. This would not be surprising, because at the time, the predominant dietary wisdom was to eat less fat. Nesheim points out that two important reports just before the 1990 guidelines – one from the National Academy of Sciences and one from the American surgeon general – both recommended reducing their fat consumption.
I'm old enough to remember all of this, and I too was convinced that fat was a big part of the problem. There was ample evidence to support this idea. I even wrote a book about low-fat foods in the Pleistocene era. I asked Nesheim if there had been a retreat at the time. "I do not remember much backflow," he says, with the warning that a long time ago.
The problem that critics focus on, however, is not simply that the percentage of calories from fat has decreased. That's why we turned to sugar and refined grains. Marion Nestle, a professor of nutrition at New York University, calls it the "Snackwell Phenomenon" which she says has surprised the nutrition community.
Nestlé published the 1988 Surgeon General's report on nutrition and health, in which it recommended reducing fat. She told me that if people reduced meat and dairy products to avoid saturated fats, they would automatically turn to healthier alternatives, such as fruits and vegetables. would eat fewer calories in general. Instead, the food industry has replaced sugars with sugars from the fats found in processed foods and consumers. Snackwell fat free and high in sugar proved to be more popular than, for example, lentils.
In fact, the consumption of sugar and refined carbohydrates has increased (27% sugar between 1980 and 1999, culminating in 1999, and 36% flour and cereals at about the same time). But over the same period, we ate more of everything and total calories increased by 24%. Little wonder, we gained weight. "The point," says Nestlé, "these are calories."
The guidelines have always advised to limit sugar. They also encouraged a high intake of vegetables and calorie levels consistent with a healthy weight. The lesson is not that the recommendations caused the obesity, but rather that we take all the little dietary advice that allows us to eat what we want and ignore the rest. All those who actually followed the guidelines did well.
The low fat recommendation was dropped in the 2015 guidelines, reflecting a generalized shift in spirit in the world of nutrition, but this change of mind has hit the climate well before. it is not applied in the directives; Consumption of sugar and refined grains has been declining for almost two decades, with fat consumption increasing. If you adhere to the theory of "low fat made us fat", you expect to see our waistline reversed. But at that time, obesity had risen by nearly a third, from 31% to 40%. It's pretty clear that we Americans can overeat any combination of macronutrients.
I asked Nina Teicholz, assistant professor at the NYU and author of "The Big Surprise: Why Butter, Meat and Cheese are Part of a Healthy Diet," about the # 39; enigma. "There is a considerable body of evidence – far superior to other diets – that shows that if you reduce carbohydrates, you can reduce obesity," she told me. A prominent critic of the dietary guidelines, she was pleased to see the 2015 iterative dropping board aimed at limiting fat, but asks: "why not include a low-carb diet" alongside other modes of diet that get the government imprimatur?
Many studies have reviewed food research and found that diets low in fat and carbohydrate are about as effective (which of course is not very effective at all), and I asked Teicholz about this subject. She pointed out that most of them are not low in carbohydrates: "This type of analysis does not manage to make the efficiency much greater when it falls to 20%. [of calories from carbohydrates] or less."
In the super-low carbohydrate diets, the lowest carbohydrates are ketogenic, which means that the low carbohydrate reduces the blood sugar level to the point that your body converts the stored fat into ketone bodies, which are then used as fuel. If you are looking for weight loss trials comparing ketogenic diets to other diets, you will only find a handful. Some showed significantly better results for the keto, but a study conducted in 2013 showed that ketogenic subjects lost only two pounds more than those on a low-fat diet during one to two year studies. More recent reviews find that either there is no difference for weight loss, or that there is a small difference in the short term, but that it does not last.
To be sure of not missing anything, I checked with a couple of people halfway through the evidence. Kevin Hall is a researcher and section chief at the National Institute of Diabetes and Digestive and Kidney Diseases, and Stephan Guyenet is an independent obesity researcher and author of "The Hungry Brain: Challenging the Instincts That Make Us Eat Too Much".
"When you advise people to cut down on carbohydrates, count calories, or recommend a low-fat diet, in the first few weeks to a few months, people tend to lose more weight on a diet with less carbohydrates. Hall said. "All of these diets are also poor for long-term weight loss."
Hall and Guyenet both think that the most likely reason is simply that people eat fewer calories; There is no metabolic magic that increases caloric expenditure. "You can make extremely important changes in fat and carbohydrate while maintaining the same protein content. There is very little caloric change, "says Hall.
This does not mean that changing your body's fuel source from glucose to ketones has no effect. "There are other things happening," says Hall. A ketogenic diet can affect glucose, insulin and blood lipids, and it has been proven that it can help manage diabetes.
Both Hall and Guyenet point out that advocates for extremely low fat diets (which include about 10% of your total calories) also report remarkable results. A long time ago, in the 1950s, the Rice Diet, which was almost entirely composed of carbohydrates, reversed the kidney disease that systematically killed, then was used to lose weight. "It's at the extremes that magic operates," explains Guyenet.
However, few of us are able to stay on these extremes in the long run, and Hall points out that we do not know if these diets are safe in the long run. In the meantime, we are examining the restriction of carbohydrates in garden varieties and ask, like Teicholz, if this type of eating behavior should not be included in dietary recommendations.
"For some people with certain conditions, it can be the diet of choice," says Hall. But the evidence is not yet "up to the recommendation of a population to do so". For Teicholz, this first part is important. Should not the guidelines take into account the fact that so many Americans have diabetes or some sort of metabolic dysfunction?
This is an excellent question. The evidence for the plans that are included in the guidelines is not particularly strong either, and the more choices we have, the better. For a diet to make recommendations, it must be defined specifically and must meet all nutrient requirements. So there are some technical hurdles, but I hope that the advisory board of the next version will take care of it.
As for the original question, I have to say no, the guidelines did not make us fat. I would go so far as to say that advocates of low-carb diets might be better at persuading skeptics if they did not make this kind of unreasonable demand. However, reducing your carbohydrate intake seems to be a very healthy way to eat and has helped many people lose weight and manage the disease. He deserves a good look.