This story laid out the basic facts about a study that compared the metabolic effects of diets containing differing amounts of fat, protein, and carbohydrate. But we think it started off on the wrong foot. The headline is scientifically incorrect. All calories are equal (1 Kcalorie equals 4.2 K joules). The story also notes, “A diet based on healthy carbohydrates—rather than a low-fat or low-carbohydrate diet—offers the best chance of keeping weight off without bringing unwanted side effects, a study published in the Journal of the American Medical Association suggests.” That is not what the authors concluded, “In conclusion, our study demonstrates that commonly consumed diets can affect metabolism and components of the metabolic syndrome in markedly different ways during weight-loss maintenance, independent of energy content.”
We don’t think the story conveyed that this topic is hotly debated by researchers, and that there is other important evidence that deserves consideration when planning a weight loss strategy. Soliciting an independent perspective would have helped bring that evidence to readers’ attention..
Many people want to lose weight both for health reasons and to look better. However, achieving long-term weight loss is extraordinarily difficult, and consumers receive lots of conflicting advice about what they should be eating to maximize chances for success. While this study provides intriguing new evidence that there may be advantages to a diet that is lower in carbohydrate and higher in fat and protein, it’s important to recognize that participants were only followed for a month on each diet and had all food provided to them by the researchers. There is considerable evidence that when people follow the same diets studied here but prepare their own food, they achieve about the same amount of weight loss after a few years regardless of what kind of diet they are on. You can argue that the “best” weight loss diet is still the one that you have have the most success sticking with in your everyday life–regardless of its fat or carb content.
Although diets with more animal protein (e.g. Atkins) are likely to cost more, we don’t think that’s a major consideration with weight loss diets. We’ll call it not applicable.
The story adequately describes the main outcome, energy expenditure, and puts it into context, noting that the low-carb group burned about 300 calories more per day than those on the low-fat diet—”about the same as an hour of moderate exercise” — and that the low-glycemic group burned about 150 calories less than the low-fat group.
The story mentioned that despite burning more calories, the low-carb group had increases in some markers of cardiovascular disease.
The results of the study are presented with no critical analysis. Even without seeking out an outside perspective, the story could have easily thrown in a few of the caveats mentioned by the researchers themselves in the discussion section of the paper. They noted, for instance, that the test diets were provided for “relatively short duration” and that the findings from this highly controlled experiment might not be applicable to “a more natural setting, in which individuals consume self-selected diets.” An editorialist also mentioned some limitations, including the fact that subjects in the low-fat group might not have been exercising as much as the other groups.
There was no disease-mongering.
The story did not seek an outside perspective. The competing USA Today story quoted 3 other experts who provided valuable context.
The focus of the story was on different dietary approaches to weight loss.
The availability of these different diets is not in question.
A number of other studies have examined the metabolic and weight loss effects of diets with different proportions of fat, protein, and carbohydrate. The story did not mention these studies.
The story quotes one of the researchers, and we couldn’t find any evidence that it relied too much on this press release.