The Big Screaming Problem with the Low-Carb Diet Study That Has Food Experts Up in Arms

If you haven’t played around with some kind of low-carbohydrate diet by now, you’ve probably heard about it from someone who has. And many of them probably say the same thing: "it’s so easy to lose weight this way."


Such anecdotal reports found support in a study published this September in the Annals of Internal MedicineThe study found that people on a so-called “low-carb” diet lost an average of eight pounds more, over a 12-month period, than participants on a so-called “low-fat” diet. While the study has received widespread praise, even from skeptics of low-carb dieting, there is one glaring problem with the study, according to Yoni Freedhoff, author of The Diet Fix.

In a recent post on his Weighty Matters blog, Freedhoff wrote,

“It's plainly not a low-carb diet study as the low-carb folks, though they were certainly prescribed a low-carb diet, never adhered to one, where even during their diets' honeymoon phase they were consuming over 25% of their total daily calories from carbs, a percentage that rose to 34% by year's end—both far higher than a true low-carb diet would require.”

The low-fat group meanwhile, “weren't even prescribed a low-fat diet, as a diet with 30% of calories coming from fat by definition isn't low-fat.”

Nonetheless, members of the so-called low-carb group were clearly getting fewer of their calories from carbohydrate than fat, and vice-versa. So on the face of it, the evidence appears to suggest that if members of the low-carb group had stuck to their diets better, the evidence in favor of that approach would have been even more convincing.

Freedhoff agrees, he told me via email. But this matter of following the diet, he wrote, is precisely the rub.

“The difficulty with low-carb diets isn’t in their ability to help with weight loss, but rather the difficulty practitioners have in enjoying them enough to stick with them. Simply put, most people aren’t willing to live forevermore with low-carb diets and consequently their temporary low-carb dieting efforts only lead to temporary weight loss results.”

As Freedhoff points out in his post, a low-carb diet tends to reduce one’s overall caloric intake. This is partly because more fat is consumed on a low-carb diet, and fat is satiating, which means it will curb your appetite. Many carbohydrates, on the other hand, can stimulate appetite. Freedhoff told me that low-carbers will tend to eat more protein as well, which also curbs hunger. The added protein might be related to why, in the study, members of the low-carb group gained muscle mass even as they lost weight, while members of the low-fat group lost more muscle mass than fat.

The low-carb group also saw improvements in various metabolic markers in their blood, including inflammatory markers, triglycerides and HDL. These findings, Freedhoff noted, are consistent with the results of other low-carb diet studies.

Aside from the issue of whether people can stick to a low-carb diet, the entire low-carb concept can be interpreted in different ways. Taken to its literal extreme, it can mean avoiding fruits, vegetables and other whole foods that contain starch, sugar and other forms of carbohydrates. Extreme practitioners of the zero-carb idea include followers of the infamous Atkins diet. Many don’t even eat fruit, which can have a lot of sugar.

Some low-carbers draw the line at processed carbohydrates, making a distinction between carbohydrates from whole plants and from processed foods. They embrace produce with open mouths, despite many vegetables, such as carrots, yams and squash, having not only starch but sugar.

Processed foods like flour or juice are shunned by many, if not most, low-carbers. Such foods are processed by means that remove fiber and break carbohydrate chains into smaller pieces, making them more sugar-like.

While Freedhoff sees many benefits of a low-carb diet, he doesn’t think it’s for everyone. In fact, he doesn’t think any diet is for everyone.

“One person's best diet is undoubtedly another person's worst, and that folks who are stuck dogmatically promoting only one 'best' diet can be safely ignored.”

Everyone has different genes and different lifestyles, with different metabolism, activity levels and life histories. These differences determine what kind of carbohydrate load they need, and can handle. And there are quality of life issues as well, Freedhoff pointed out.   

“If a person doesn’t like the life they’re living while they’re losing weight, even if they lose a whole bunch, they’re not likely to keep living that way. Food of course isn’t simply a fuel source. It provides us with comfort, it serves us in celebration, and it is the world’s oldest social network. If a person’s dietary regime takes those roles of food away from a person, the likelihood of them sticking with it is very low.”

At the very least, Freedhoff blogged, the study further refutes the idea that dietary fat causes heart disease and obesity.

An “overarching take-home message from the study,” he wrote, is that “overly saturated-fat phobic national dietary guidelines that still steer people to diets consisting of 55% carbohydrates probably aren't necessary.”

While decades of dietary guidelines have been based on a connection between dietary fat, obesity and heart disease, evidence that’s accumulated in recent years suggests it’s a lot more complicated than has long been assumed. Many foods developed to be low in fat are infused with sweeteners, in an effort to make them more palatable. But evidence is mounting that sugar contributes more to heart disease and obesity than the fat they were brought in to replace.

So, everything in moderation, including fad diets. Still, if you haven’t played around with your dietary carbohydrates, it might be worth your while. And while limiting one’s intake of processed carbs may be a good idea, it doesn’t mean you should always say no to a good slice of pizza.

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