The big news story in the newspaper and on TV this week was all about a new diet study published in The BMJ. This peaked my interest so I paid close attention to the findings. Medical doctors were on TV singing the praises of this new study as revolutionary for dieters! They reported that the study results had found that low carbohydrate, high-fat diets were in fact the best way to lose and maintain weight loss. Many of you know I am not a fan of this type of diet so I decided to read the original research and draw my own conclusion. Here is what I found.
- The study was divided into three group: high carbohydrate, moderate carbohydrate and low carbohydrate diets. Each participant had food prepared for them which took away that confounding factor. I applaud that effort, however, what they fail to mention is what kind of carbohydrates were included in the study. Did the high carbohydrate diet consist of highly processed, high-glycemic load carbohydrates or were they fruits and vegetables in whole form? That is a really important part of the validity of the study and the inability to report this is a red flag to me. Furthermore, did the three groups eat the same types of foods just in different proportions or did they eat entirely different foods? This, again, would make a huge difference to the validity of the findings.
- One of the authors claims is that calories do not make the difference in weight loss and maintenance but rather the type of calorie. In essence they claim that calorie restriction isn't important. However, in the first phase of the study the particpants were required to lose weight. What method did they use to help the participants lose weight? You guessed it, calorie restriction! There goes their argument!
- The authors of the study claim real world applications or "external validity." I would argue that this might not be the case. They started their study with 1,685 participants. Of those 1,685 screened (also can't figure out the screening process) only 234 were allowed to participate. Of that subset only 164 were able to achieve the 12% weight loss in the initial phase of the study that was required before they could move on to phase two. This creates a very small subset of people that a low carbohydrate diet might work for so in my opinion this is not a study that can be widely generalized to the obese population.
- When reading the study I noticed that during the test phase when participants were in the three groups, calories were adjusted constantly to maintain within 2% of the original weight loss achieved in the first phase. What????? I thought they were trying to prove that calories restriction was not the answer yet they manipulated the calories again!
- The study did not account for several key factors. The first is exercise. The low carbohydrate group was said to have expended 200 calories a day more than the other groups which is supposed to prove that this group would have an easier time maintaining weight loss. However, the authors failed to account for the amount of exercise among the participants so this increase in caloric expenditure could be from exercise. Additionally, body composition affects calorie expenditure. A person with a higher muscle mass will also have a higher calorie expenditure secondary to the fact that muscle is more metabolically active than fat. That might have been a good thing to consider! Lastly, the authors glance over the fact that the participants that had the greatest caloric expenditure were also the participants that had the greatest adherence to the study and had the least insulin sensitivity at the start of the study.
The lesson here is two-fold. First, don't believe everything you hear or read. Be a smart consumer and if it seems to good to be true then perhaps it is! Second, the diet that can claim the longest lived and healthiest people is one that is based on whole foods that are largely plants. That research can be found in numerous studies and books like the China Study. That research doesn't have ties to pharmaceutical companies or a large corporation interested in making money off of their research. You chose which one you want to believe!