The New York Times (NYT) published an article titled: A Call for a Low-Carb Diet That Embraces Fat. The study presented – Effects of Low-Carbohydrate and Low-Fat Diets – was conducted by the National Institutes of Health (NIH). In the article it’s argued that dietary guidelines should push away from fat reduction and instead encourage reduction of processed foods and refined carbohydrates.
The conclusion of the study was: “The low-carbohydrate diet was more effective for weight loss and cardiovascular risk factor reduction than the low-fat diet. Restricting carbohydrate may be an option for persons seeking to lose weight and reduce cardiovascular risk factors.”
It’s already well established that low-carb/high-fat diets can be effective for weight loss. The second premise – that a low-carbohydrate diet reduces cardiovascular risk – is more interesting and controversial.
First thing’s first, what were the diets?
- The low-carb group averaged about 105g of carbs per day. That’s not exactly a low-carb diet when the target was supposed to be below 40g.
- The low-fat group averaged about 28% of calories from fat per day. That’s not exactly a low-fat diet, though that was within target.
Already we see a bias present – this is an advantageous comparison. The study doesn’t justly compare a low-carb diet to a low-fat diet.
It’d be really interesting to analyze what the participants were actually eating; the instructions were pretty vague: the low-carb group were told to maintain intake of carbs to less than 40g, and the low-fat group were told to maintain less than 30% of their calories from fat. Here we see another problem: the low-carb diet was more restrictive, and restrictive diets usually always result in greater weight loss. Participants were told to not restrict calories, though the low-fat group did consume slightly more calories than the low-carb group (but a statistically insignificant difference of 2,034 versus 1,998).
Honestly, I don’t think this study does the low-carb movement enough justice because the weight loss was really small – just 5.3kg average over one year. A well managed low-carb diet can induce much more weight loss than that, but then so too can a well managed low-fat diet. Also note that in both groups there was an initial weight drop and then weight gain; this is typical of what we see in most diet-based studies as the weight loss isn’t usually sustainable long term.
The cholesterol markers are interesting but not at all surprising. Since the low-carb group had greater weight loss it would be expected that they had lower total cholesterol than the low-fat group, which is what occurred. The low-fat group had higher LDL, which is to be expected considering they were following the standard dietary guidelines packed with processed foods, refined carbohydrates and refined fats. Also unsurprisingly the low-fat group had higher triglycerides, likely due to higher sugar consumption. At the end of the study, both groups were still overweight, were no longer losing weight and had poor heart health based on the cardiovascular risk factors measured.
If processed foods were eliminated in both groups we would have seen more dramatic weight loss in both groups, but that’s not what was studied. This certainly isn’t supportive evidence that a high-fat diet is ideal and it doesn’t support the NYT headline calling for an embrace of fat.
From the NYT article, Dr Mozaffarian states: “in a free-living setting, cutting your carbs helps you lose weight without focusing on calories. And that’s really important because someone can change what they eat more easily than trying to cut down on their calories.” This is a good point, but what’s also important apart from just weight loss is long term good health, which hasn’t yet been proven for low-carb or high-fat diets. Is shifting focus from calorie counting to carbohydrate counting any better? Evidently not. Many diets work for weight loss, not just high-fat diets, and restricting calories isn’t the only other solution.
In opposition to Mozaffarian’s view, an obesity physician Dr Freedhoff points out: “the idea that people should eat a low-carb diet is not new. And it has failed time and again in the past because, again, most people can’t live like this … we tried restrictive, low-carb eating during the Atkins boom … In the year 2000, it is estimated that one in five American households had one member who tried Atkins. If these diets were sustainable we would still see one in five families on it and we’d see improvements in the national waistline. We haven’t seen that.” We see this even in this study – most weight loss efforts were lost in the end after 12 months. The low-carb group also had a higher drop out rate compared to the low-fat group (though not statistically significant, 20% versus 18%).
Continuing from the NYT: “[T]he research suggested that health authorities should pivot away from fat restrictions and encourage people to eat fewer processed foods, particularly those with refined carbohydrates.” This again isn’t a new or controversial recommendation. Rather than “pivot away” though we should just put more focus on recommending elimination of processed foods and refined carbohydrates. Refined carbs are bad, okay?
The moral of the study: processed foods and especially refined carbohydrates are detrimental to both health and weight loss. Who would have thought? Thankfully we have this study to provide such a groundbreaking conclusion!