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When it comes to losing body fat, the gold standard is to combine exercise and nutrition. The goal is to eat in a way that allows you to train hard, preserve muscle mass, and achieve an energy deficit.

Several different exercise/diet combinations have proven effective but very low carb diets are generally avoided due to the fear that exercise performance will be compromised. Glucose is the body’s preferred energy source for high-intensity exercise and the theory goes that a keto diet that deprives the body of glucose in the form of dietary carbs will lead to reductions in training quality. There is also a fear that lack of carbs will compromise lean mass gains compared to higher carb diets.

In reality, the effect of low-carb keto diets on performance and body composition outcomes is not so cut and dried. For example, a study that used well-trained college-age men and put them on a keto diet or a traditional higher carb diet for 10 weeks found similar improvements in strength and power performance between the groups (1). Meanwhile, the keto diet group lost 2.2 kg of body fat and increased lean mass by 2.4 percent, whereas the higher carb group lost 1.5 kg of body fat and gained 4.4 percent lean mass.

The study authors concluded that the keto diet can be effectively used to reduce body fat and improve body composition without compromising performance. If mass gaining and hypertrophy are the primary goal, then a higher carb intake is recommended.

Other recent studies done on men show similar outcomes. But what about women?

A common belief is that keto diets are harder for women to follow due to women’s greater reliance on glucose at rest than men. In fact, recent studies show women can benefit to a similar degree from keto diets combined with anaerobic training protocols. For example, a recent study from Spain tested the effect of an 8-week keto diet or a traditional high-carb diet in conjunction with a strength training program on trained young women (2).

The dietary intake in each group was as follows:

Keto Diet Traditional Diet
Protein Grams 115 g 97.3 g
Protein % Calories 26.8% 19.7%
Carbohydrate Grams 38.6 g 282 g
Carbohydrate % Calories 9% 57%
Fat Grams 121.7 g 51.3 g
Fat % Calories 64.1% 23.3%
Daily Calories 1710 1979
Cal/KG/Fat Free Mass 40.1 45.5

Participants were allowed to eat ad libitum, meaning they did not need to restrict calories. They trained four days a week, following an upper/lower body split periodized training program.

Results showed that the keto diet group lost an average of 1.1 kg of fat mass but also lost 0.7 kg of fat free mass. Performance on strength tests improved moderately:
  • Bench press 1RM improved by 1.5 kg
  • Squat 1RM improved by 5.6 kg
  • Countermovement jump improved by 1.6 cm
The high-carb diet group increased body fat by 0.4 kg and gained 0.7 kg of fat free mass. They also had significant improvements in strength performance:
  • Bench press 1RM improved by 4.6 kg
  • Squat 1RM improved by 15.6 kg
  • Countermovement jump improved by 2.2 cm
Researchers noted that the fat loss in the keto group was due to increased satiety, which allowed the women to consume significantly fewer calories than the higher carb group. Ketones—the primary metabolic fuel source during a keto diet—blunt hunger, leading people to automatically eat fewer calories. The takeaway is that a keto diet is a great tool for women who want to lean up without “dieting.” Intentional calorie restriction can do a lot more harm than good if it depletes essential nutrients and leads to increases in stress and anxiety. Fat loss shouldn’t be an all the time thing, so you can employ a low-carb, high-fat diet for a training cycle to get rid of excess fat, and then get back to more performance-focused eating. Higher carb diets will generally be your go-to choice when putting on muscle or maxing out your strength gains are the goal. If you’re interested in learning more about how a keto diet impacts training outcomes, check out our new ebook The Keto Diet Handbook that is packed with research on training on keto. References: 1. Wilson, J., et al. The Effects of Ketogenic Dieting on Body Composition, Strength, Power, and Hormonal Profiles in Resistance Training Males. Journal of Strength and Conditioning Research. 2017. 2. Vargas-Molina, S., et al. Effects of a ketogenic diet on body composition and strength in trained women. Journal of the International Society of Sports Nutrition. 2020. 17(19).