Kristi Storoschuk, BSc (Hons.) is a science communicator with a research focus on ketogenic diets, metabolic therapies, and fasting for health optimization. She currently works alongside the world’s leading ketogenic researchers providing scientific education for the mainstream audience. Outside of her research, you will find her traveling the world, doing CrossFit, and optimizing her health through diet and lifestyle.

If reaching ketosis while fasting is a proxy for fat-burning, we totally understand why you might think you need to be in ketosis to lose weight. The good news is: you don’t! Ketosis is certainly a product of accelerated fat burning, however, we still burn fat in the absence of ketones. Reaching ketosis is not necessary for fat loss.

It would be easier if we could say with authority that at any given moment you are burning either fat or sugar, but the truth is humans are never burning one fuel exclusively. At rest, around half of our energy is generated from burning fat, the other half, mostly carbohydrates, but these contributions are influenced by the fed- and fasted-state. During a fast, we rely more heavily on body fat to support our energy needs. As a fast progresses, fat is burned at an accelerated rate, and the breakdown products of fat are used to make ketones. This is because our brain can’t use fat directly as fuel like most of our other tissues can and relies on ketones as an alternative to glucose during prolonged periods of fasting.

So, increasing ketones does correlate with increased fat burning while fasting, but, it is not required to burn fat, and therefore isn’t required to lose weight. Maintaining a Caloric deficit over time is the primary driver of weight loss, and intermittent fasting is an effective strategy for achieving this! 

Parsons, S.A., Jones, K.P., Yi, F. et al. 2016. A novel clinical approach to evaluating changes in fat oxidation in healthy, overnight-fasted subjects. Transl Med Commun 1, 6.

Melzer K. 2011. Carbohydrate and fat utilization during rest and physical activity. E Spen Eur E J Clin Nutr Metab. 6(2):e45-e52.  

Thanks to Debbie G., Beth A., and Allison M. for submitting similar questions! 

Is it Necessary to Reach Ketosis to Lose Weight? 

Is it Necessary to Reach Ketosis to Lose Weight?

Thanks to Samari S. for this question.

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