Low-Carb Diets: Quit Drinking the (Sugar-Free) Kool-Aid
There are few areas of scientific research murkier than nutrition. Thousands of studies have tackled the seemingly simple question of what we should eat in order to lose weight. But one study that points in one direction is inevitably countered by another pointing in the opposite. Every tiny change in study design could sway findings one way or the other. The result is maddening. Sifting through the literature reveals no overarching consensus beyond "eat less," "move more," and "go easy on the sugar."
But what about this never-ending "low carbohydrate" fad? Advocates of "Paleo," "Zone," or "Atkins," -- all forms of low-carb diets -- say that eating fewer grains produces more weight loss and better health outcomes than basic reduced-calorie diets.
Here again, scientists are conflicted. Some studies show that low-carb diets vastly outperform balanced, calorie-restricted diets, but other studies show no difference at all.
The best tool we have for detecting a pattern in the literature is the systematic review, where similar studies are grouped together and analyzed. If you're wondering whether low-carb diets are better than traditional weight loss diets, you're in luck. Researchers just completed a systematic review to answer that very question.
Scientists based out of Stellenbosch University poured through published records to find studies in which low-carb and balanced diets were directly compared. The team was very selective, including only randomized, controlled trials where the two comparison diets had the same number of calories, featured at least 10 subjects per group, were longer than 12 weeks (with long-term follow up), and were solely focused on diet. Only 19 studies survived the purge.
In these studies, subjects consuming low-carb diets received roughly 35% of their calories from carbohydrates, 35% from fat, and 30% from protein. Those consuming balanced diets received 55% from carbohydrates, 30% from fat, and 15% from protein, in line with government recommendations.
The review showed that both low-carb and balanced diets yielded similar weight loss in the long-term, with low-carb diets edging out the competition by a single pound after 1-2 years (a statistically insignificant amount). Differences in improvements to other health variables like cholesterol, triglycerides, and blood pressure were almost imperceptible.
In short, the review revealed that the purported revolutionary benefits of low-carb diets are likely overstated, and any associated weight loss results almost entirely from accompanying calorie restriction, not from specifically cutting out carbohydrates.
"It follows that when considering dietary strategies for weight loss, less emphasis should be placed on an ‘ideal’ macronutrient composition and more emphasis on reduction in total energy intake," the researchers state.
Advocates of low-carb diets are technically correct about one thing: a calorie is not just a calorie. Protein, fat, and carbohydrates -- the three primary macronutrients -- are used by the body and transformed into energy in different ways. But those distinctions are -- when it comes to weight balance -- miniscule, and do not translate to anything game-changing for the health of modern humans.
Source: Naude CE, Schoonees A, Senekal M, Young T, Garner P, et al. (2014) Low Carbohydrate versus Isoenergetic Balanced Diets for Reducing Weight and Cardiovascular Risk: A Systematic Review and Meta-Analysis. PLoS ONE 9(7): e100652. doi:10.1371/journal.pone.0100652