PrintAre Carbs More Fattening Than Fat?

Avoiding carbs is in – from updated menus to celebrity diets, more and more health-conscious individuals are ditching carbs and opting to eat more fat.

Because they often contribute to weight gain when consumed in excess, the carbs and sugars people eat have recently garnered attention and lead to a fundamental question: Are carbohydrates more fattening than fat?

The conventional wisdom suggests that there shouldn’t be any difference in whether or not weight loss is achieved by cutting calories from either carbs or fat. If a calorie equals a calorie, then reduction of energy intake from either should lead to weight loss.

However, some have argued that carbs could cause more weight gain due to their effects on insulin. After all, insulin is the hormone that promotes the accumulation of storage of adipose tissue (body fat) as a result of overeating carbohydrates.

But while the carbohydrate-insulin model proposes that replacing carbs with fat should reduce insulin secretion leading to greater fat burning, the hypothesis hasn’t quite held up to scrutiny when put into practice in scientific studies.

Low-Carb Versus Low-Fat Diets

One of the most recent trials was designed by Kevin Hall of the National Institutes of Health, who investigated whether a low-carbohydrate ketogenic diet led to increases in energy expenditure, greater body fat loss, or positive changes in body composition as compared to a low-fat diet (1).

Using a crossover design, the study put 17 overweight or obese men on a high-carbohydrate baseline diet for four weeks followed by a low-carbohydrate ketogenic diet. Everything else in their diets was held constant, including dietary protein.

All diet phases were strictly controlled under metabolic ward conditions – the gold standard in nutrition research – and the researchers also measured average energy expenditure using doubly labeled water, considered state-of-the-art for this kind of study.

At the end of the study, Dr. Hall reported that all the subjects had lost weight throughout the study corresponding with the reduction of calories. Compared with the low-fat, higher-carb diet, the low-carb ketogenic diet coincided with a barely detectable increase in energy expenditure and a decreased metabolism.

Body fat loss also slowed while on the low-carb ketogenic diet (despite lower insulin levels) coinciding with increased losses of fat-free mass and use of protein for energy, Dr. Hall and his colleagues wrote.

Corroboration of Results

The research corroborated earlier results from studies performed by Dr. Hall along with those of other scientists from other universities (2-3). One of those trials from Carol Johnston at Arizona State University found that both low-carbohydrate ketogenic diets as compared with typical low-fat diet were equally effective in leading to weight loss.

However, Dr. Johnston and her colleagues reported that the low-carb ketogenic diet was “associated with several adverse metabolic and emotional effects,” which included adverse results for lipid profiles along with poor mood states in subjects.

Does the mean carbohydrates are off the hook for weight gain? No, because it’s also well known that the majority of expendable calories do come from carbohydrate-rich and sugary foods, drinks, and desserts.

Additionally, there are some individuals who might benefit from low-carb ketogenic diet. Some evidence from animal and human studies suggests that a low-carb ketogenic diet may be beneficial for those with epilepsy or in situations when metabolic complications (e.g. insulin resistance) or cardiovascular risk factors are involved (4).

The research does suggest that it’s important that a balanced approach toward reducing calories is warranted for healthy weight loss. Carbs and insulin are not inherently fat producing on their own. The context in which carbs are consumed matters, in terms of energy balance.

Moreover, eliminating an entire macronutrient from the diet not only could have a person miss out on foods with important vitamins, minerals, phytonutrients, and fiber, but also may not be any more effective for weight loss.

References

  1. Hall KD, Chen KY, Guo J, Lam YY, et al. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr. 2016 Aug; 104(2):324-33.
  2. Hall KD, Bemis T, Brychta R, et al. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metab. 2015 Sep 1;22(3):427-36. doi: 10.1016/j.cmet.2015.07.021. Epub 2015 Aug 13.
  3. Johnston CS, Tjonn SL, Swan PD, White A, Hutchins H, and Sears B. Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets. Am J Clin Nutr. 2006 May; 88(5):1055-1061.
  4. Kosinski C, Jornayvaz FR. Effects of ketogenic diets on cardiovascular risk factors: Evidence from animal and human studies. Nutrients 2017, 9(5), 517; doi:10.3390/nu9050517