Two weeks ago, another major shot was fired in the war between those who believe that decreasing carbohydrates are essential to weight loss, and those who believe low carb is no better than any other method of weight loss.
The study, by all accounts, was impressively executed (at the cost of $12M), and was designed to determine whether low carbohydrate diets had any advantage in terms of total energy expenditure as compared with medium and high carbohydrate diets. Simply said - is there a metabolic advantage, where your basal metabolism burns more energy per total calories consumed on one diet vs the other.
Advocates of the low carb approach to weight loss and weight maintenance subscribe to a physiological theory known as the carbohydrate-insulin model of obesity, where increased the increased ratio of insulin to glucagon after high glycemic meals directs fuels into storage in adipose tissue. The rapid storage of fuels as fat leads to increased hunger and food cravings, and decreased energy expenditures, predisposing to weight gain. In this model the degree of weight gain should correspond to the insulin level - as higher insulin levels lead to greater fuel storage. The theory provides an explanation for the global obesity trend as people have increased their consumption of high glycemic refined carbohydrates over the past 30 years.
The theory has some eloquent supporters, most notably journalist Gary Taubes, who founded the Nutritional Science Initiative (NuSi) to do the science necessary to prove or disprove the theory.
Until now, existing data has not provided support for this theory, with perhaps the greatest challenge coming from a NuSi study led by Kevin Hall, which was done under the controlled settings of a metabolic chamber.
Despite the lack of evidence from controlled feeding studies, supporters of the carbohydrate:insulin theory have maintained that studies were not long enough - most were only two weeks, and the process of adaptation to a low carb diet takes at least 2-3 weeks - or they were technically flawed (or both).
On the other side of the debate, many researchers and nutritionists point to the many real-world studies that have failed to show that low carb has any benefit over any other approach (ie. Mediterranean diet, Zone, low fat, etc.).
Since the study was about weight maintenance, all subjects (164 adults aged 18-65 years with a BMI >25) were put on the same weight loss diet with the goal of 12% weight loss (within 2%).
After the run-in weight loss, the subjects were randomized to to three test diets according to carbohydrate content (high, 60%; moderate, 40% or low 20%). Each test diet was controlled to deliver the same amount of protein (20%) and were adjusted to maintain weight loss.
The results were supportive of the carbohydrate-insulin model:
While these results seem to confirm the carbohydrate:insulin hypothesis, other researchers are not yet ready to concede. Kevin Hall, the researcher that led the original metabolic chamber, NuSi trial that failed to demonstrate any metabolic advantage to a low carb diet, and a known skeptic of the carbohydrate:insulin theory, has pointed out a potential methodological issue with the trials. He points out that the method that the researchers used to measure energy expenditure is less reliable when weight is changing - so the proper comparison for diet effect should be the difference between energy expenditure at the beginning of the trial, before any weight loss, compared to the weight at the end of the trial. Instead, the study compared the effects after the weight loss, and before randomization into the three experimental groups. If you look at the data from Hall's viewpoint, the metabolic advantage shrinks to less than 100 calories - an effect that may not be statistically significant.
Others point out that in the real world low carb diets do not outperform other diets when it comes to weight maintenance, and that this trial screened over
Still these findings are intriguing as they provide some evidence for the claim made by low carb proponents that low carb is easier than any other diet.
So the jury is still out...
If we summarize some of what we know about low carbohydrate diets:
While there are debates about LCHF and LFHC - there should be no debate that a HFHC is the real issue in our society today. Too many people are eating too many calories from poor quality sources high in both fat and carbohydrates. This simply put is the cause of obesity in our society.
Try as we might to learn more about nutrition, nothing beats the the simple rules laid out by Michael Pollan, in his book "In Defense of Food":
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Dr. Brendan Byrne