Are Low Carbohydrate Diets Bullshit?

March 30, 2014 § 1 Comment

I had a day off work in the middle of the week so I decided to write a little blog on a topic I don’t typically focus on: health. Specifically the usefulness of limiting carbs when “cutting” or trying to decrease body fat. If you ask the bodybuilding community you will find that the universally accepted broscience answer is a resounding “yes”. According to common knowledge, limiting your carb intake is a sure fire way to speed up fat loss. Of course, it’s also universally understood that maintaining a calorie deficit is the most essential step to fat loss. The focus of this post will be to confirm or deny the commonly accepted claim that limiting your daily carbohydrate intake will speed up the rate at which you lose body fat assuming that you are already on a calorie deficit diet.

As it turns out, the bulk of the independent research done on low carb dieting supports the broscience postulate that lower carbs = quicker fat loss. Even a periphery glance at the data should confirm that.

In one study 322 moderately obese men were randomly assigned one of three different diets over a two year trial period (low fat diet with restricted calorie intake, Mediterranean diet with restricted calorie intake, or low carbohydrate without restricted calorie intake). Over a two year period the results showed that those participants on a low carbohydrate diet lost more weight despite the fact that they weren’t even restricting their calorie intake. (See Figure below)

Study1

The next obvious question is whether or not these results hold up when tested on non-obese individuals. And sure enough, they do. In a meta-regression of over 87 studies it was found that:

“After control for energy intake, diets consisting of ≤35–41.4% energy from carbohydrate were associated with a 1.74 kg greater loss of body mass, a 0.69 kg greater loss of fat-free mass, a 1.29% greater loss in percentage body fat, and a 2.05 kg greater loss of fat mass than were diets with a higher percentage of energy from carbohydrate. In studies that were conducted for >12 wk, these differences increased to 6.56 kg, 1.74 kg, 3.55%, and 5.57 kg, respectively.”

Even studies which attempt to brush aside the importance that low carb diets have on fat loss show a marked difference between low carbohydrate and other diet types. In a study which assigned 811 “overweight” adults to one of four diet types

“…the targeted percentages of energy derived from fat, protein, and carbohydrates in the four diets were 20, 15, and 65%; 20, 25, and 55%; 40, 15, and 45%; and 40, 25, and 35%.”

Despite the fact that the carbohydrate levels weren’t actually very low (many body builders will reduce carb intake to much lower than 35% while on a cut) the results still indicated an obvious benefit to low carb diets and their effect on weight loss versus other diet types. (See this figure)

Even with the evidence provided above, the most the researchers were willing to say was that “reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize.” Well no shit.

And finally there’s those half-assed meta-analyses which are mind-blowingly short on detail or actual research that seem to make wide ranging claims based on very shaky evidence at best. Here’s a good example. A supposedly “systematic” review of research led to the conclusion thatweight loss achieved is associated with the duration of the diet and restriction of energy intake, but not with restriction of carbohydrates.”

The only problem is that this “systematic” review consisted of two cherry picked studies which according to the studies themselves were limited by “a high dropout rate” and “suboptimal dietary adherence”. The original meta-analysis also failed to mention that the low carb diet was not energy restricted (i.e. at a calorie deficit). Furthermore, the original study states that participants on a low carbohydrate diet had “more favorable outcomes” after a year than those on a conventional diet. All this, I might add, even though the low carb dieters were not on a calorie deficit diet.

So are low carb diets worth it?

If you’re otherwise healthy and trying to cut your body fat percentage, I would unequivocally recommend a low-carb diet. This isn’t a recommendation for eliminating carbohydrates from your diet or support for a ketogenic diet. However, I believe that the current research provides plenty of support for the generally accepted broscience maxim that a low carb diet is more effective at decreasing overall body fat while maintaining a hypocaloric diet.

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