What is the best diet for weight loss?

Brennan Smith, PhD

Brennan Smith, PhD

Following a diet plan (or “dieting”) can be defined as following a restricted course of food intake in order to lose weight. Diet plans can be designed to promote the inclusion or exclusion of a given macronutrient.

There are three macronutrients in the human diet; Fat, carbohydrate and protein. Many diets aim to change the balance of these three components in order to promote weight loss. Some of the most popular diet plans focus on reducing carbohydrate (low carb), or reducing fat (low fat).

The first recorded diet plan was designed for King William I (1028-1087 CE), who suffered from severe obesity to the point where he was unable to mount a horse. This led him to adopt the liquid diet, although in actuality he followed a liquor-based diet. Indeed, for the better part of a year the King of England subsisted primary on alcohol. This plan worked moderately well to the point where he was able to mount a horse again, however in ironic fashion he was killed when his horse reared while he was potentially under the influence. Unfortunately, his casket was still too small and therefore this story is not only about the first diet, but also about the first failed diet, in addition to highlighting the dangers of operating a vehicle while under the influence of alcohol.

Fast forward a few centuries and we pass by a number of compelling diet plans such as the Cabbage Soup Diet, Fletcherism (chewing diet) and the Banting diet. Then, in the 1970s a number of prominent nutrition publications were released highlighting the negative health effects of fat consumption, especially saturated fat. These publications started a war on fat and many food companies began reducing the fat content in their products and carrying the label “low fat.” However, to make the low fat products palatable, sugar was added and thus began the low fat diet fad of the 1970s.

The conversation began to shift in 1992 when Dr. Robert Atkins wrote the second version of his diet plan in a book called “Dr. Atkins New Diet Revolution.” This diet plan stressed that carbohydrates were the enemy of the body, not fat, and this standpoint quickly gained momentum. The idea that carbohydrate should be heavily restricted has led to other low carb dietary strategies including the “Paleo diet” which has been popularized by Dr. Tim Noakes in his book “The Real Meal Revolution.” While doctors published books detailing the benefits of low carb diets, the scientific proof had yet to be observed. Indeed, attempting to tease out whether a low carb diet was better than low fat has proven to be a very tricky scientific question.

To get at whether low fat or low carb results in more weight loss, data from the health monitoring app “MyFitnessPal” was collected and analyzed. Data from 4.2 million users who had entered weight loss targets was examined to observe what dietary trends were present in the people who accomplished their weight loss targets vs. those who did not. Interestingly, researchers found that there was no difference in fat and carbohydrate intake between successful weight losers vs. unsuccessful. Therefore, reducing fat vs. reducing carbohydrate (and vice versa) does not correlate with weight loss success in millions of people. So if the key to weight loss is not carbohydrate, nor is it fat, what is it?

A study from 2005 published in a highly reputed journal provides an answer to this question. This study examined different diet programs, some of them low carb, some of them low fat. Upon analysis, a similar finding to the MyFitnessPal study was observed – none of the diets worked any better than the other ones. That is, the low carb was no better then the low fat and vice versa. However, this study provided additional insight – the authors collected dietary adherence data and gave a score based on how well the diet plan was followed on a scale of 1 to 10. If the subject followed the diet perfectly a 10 was recorded. If the subject cheated on their diet they would receive a lower score. When the authors examined the data a very obvious pattern emerged – the higher the adherence, the higher the weight loss – a pattern conserved across both low fat and low carbohydrate diets.

So to answer the question “What is the best diet for weight loss?” Well, it doesn’t matter which diet plan you choose. There is no miraculous feature in low carb or low fat diets, nor any other type of diet for that matter. The most important variables are 1) whether you adhere to your plan and 2) whether that plan is sustainable long term.

By Brennan Smith, PhD

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