This article is the ultimate showdown. In dieting, is a calorie just a calorie, or is there an effect from entering a ketosis state by removing most carbohydrates from the diet? There have been many fad diets in recent years, but one diet that seems to be getting more attention than most fads is the ketogenic diet. This diet is commonly confused with any diet restricting carbohydrates, but there are a few physiological keys that set this apart from the rest.
If you have read the first chalk talk article you will already be familiar with this diet, but put simply, ketosis is an induced physiological state through major carbohydrate restriction in order to produce an alternate fuel source called ‘ketone bodies’. The brain is a very picky organ that only uses carbohydrates, but when there aren’t enough carbohydrates to satisfy the brain’s energy needs, it then sets the ketone bodies as the primary fuel source. This style of diet is suspected to achieve a higher basal metabolic rate (how many calories your body burns in a day doing nothing), and burn more fat than the standard diet of calorie restriction, all backed through theories based off the carbohydrate-insulin model.
The carbohydrate-insulin model looks at the relationship between eating carbohydrates, and as a reaction the body secreting insulin driving storage of nutrients. If the organs and muscles are not depleted, than the storage of nutrients is in the form adipose tissue (body fat). The body makes adipose tissue through the creation of triglycerides, and a triglyceride is an ester composed of 3 fatty acids and 1 glycerol (carbohydrate). Some have concluded that if there isn’t enough glycerol to create triglycerides than fat accumulation will be more difficult. Other suspected effects from insulin secretion is the disruption of metabolism in the organs, so there is less energy expended during the day, and less of the energy metabolized is from fat because fat is being redirected for fat storage during these high-insulin periods.
Hall, the first author on this article has produced articles in the past observing similar experiments, where obese men either restricted fat or carbohydrates in their diets. These results showed that the fat restriction diet was superior to carbohydrate restriction at burning fat, but there was one key difference. The carbohydrate restricted diet is not the same as a ketogenic diet because the carbohydrates were not depleted enough for the body to create more ketone bodies. Hall addressed these shortcomings in the present article we are analyzing by creating a diet that would induce ketosis.
This newest study, published in July 2016, recruited 17 obese men to follow an extremely strict 8 weeks of dieting. The first 4 weeks of dieting was a standard USDA recommended diet with balanced macronutrient (fat, carbs, protein) percentages, and the last 4 weeks was a carbohydrate reduced ketogenic diet only allowing 31 carbohydrates per day, which is less than 2% of the normal recommended amount. Both diets had a daily net -300 calorie deficit assessed weekly in attempt to keep everything the same between the two diets, apart from the macronutrient change. These subjects were held to as strict as possible standards to make them follow the diet by admitting everyone into metabolic wards that confine subjects from leaving and give them the exact portions that the diets requires. In addition, there were 2-day periods in each diet where they would be locked in metabolic chambers (small rooms) to find exact energy expenditure.
Figure 1- Breakdown of 8-week dieting period
There ended up being an insignificant difference in total body weight and body fat lost, but it is important to note that in the ketogenic diet about ¾ of the weight was lost quickly in the first 15 days. This rapid initial weight loss was attributed to water loss in the body with the hypothesis that since 1 carbohydrate needs 3 molecules of water for storage. So it makes sense that the body would get rid of the excess water as carbohydrates are used up without replacement. Body weight loss was a secondary question in this article, with the researchers primarily questioning if the carbohydrate-insulin model had correctly predicted that the body basal metabolic rate would increase. The chamber did find the ketosis diet burned more calories per day, but barely within detectability (100-150 calories). This does not coincide with the 300-600 calorie prediction that came from the carbohydrate-insulin model, and the researchers found some factors that could account for the minimal difference between diets. The main factor was the unmonitored amount of physical activity subjects were doing outside of the metabolic chambers. Outside of the metabolic chambers subjects had access to stationary bicycles, and if they had been exercising harder during off days of the ketogenic diet, than this could have temporarily raised the individuals’ basal metabolic rate.
While there was a small difference in basal metabolic rate, it was certainly not significant enough for the researchers to conclude that the ketogenic diet is not better than the standard dietary guidelines. While I do believe this study’s results are highly reliable, I don’t think that this is an open and shut case. There have been other studies that have shown greater caloric expenditure when protein is increased in the diet, but in this study protein levels were kept the exact same between the two diets.
It is worth directing further research toward finding out if there is a synergistic effect from a ketogenic diet by re-proportioning the remaining two macronutrients (fat and protein) to a more balanced ratio, as opposed to the 1:1 calorie swap between fat and carbohydrates that was done in this experiment. Also, it is worth questioning why there was a greater amount physical activity during the ketogenic diet. Was it just an anomaly that the subjects increased exercise during this period or did the ketosis stimulate the urge to exercise more? Overall, this study has revealed that fat metabolism is a multi-faceted problem that will take time to understand only through careful experiments like this, isolating single variables to test theories like the carbohydrate-insulin model.