Whether you've just started a low-carb lifestyle or have been going at it for decades, the term "ketones" will spring up time and time again. As the most broken-down form of fat, when you go low-carb, ketones are used for energy throughout the day. While this is basic knowledge, however, many dieters aren't sure exactly how they function. How much do ketones truly matter, and is measuring them necessary for maintaining healthy, low-carb living? Let's set the record straight.
Ketones and Fat Loss
The keto diet provides a variety of health benefits. Whether you're a diabetic wanting to improve self-management, someone looking to manage their acne (1), or just wanting to drop some weight, this diet offers something for everyone. Becoming fat-adapted uses your body's natural energy stores to help reach these goals. Keto is also a highly effective weight loss method, allowing the the body to burn fat instead of carbs, reducing hunger, and increasing energy. This is where the ketone debate comes into play. While some dieters assume that high ketone levels result in improved fat loss, that isn't always the case.
Ketones and Fat Adaptation
While the low-carb lifestyle promotes fat loss, high ketone levels themselves won't guarantee a drastic drop in pounds. Once the body reaches and maintains ketosis, ketone levels will fluctuate based on minor changes. Once you're fat-adapted, for instance, a single slice of bread or an extra piece of fruit could throw those ketones off balance, and if you embark on a carb-heavy vacation, they could drop drastically. Once the body reaches this final stage of ketosis, however, its ability to bounce back improves, and once you return to keto, you'll see ketone levels increase. Does this enhance fat loss, however? Not necessarily.
When you measure ketones, the level in your bloodstream reveals the total amount present in the body's fuel tank, not the amount available for fat burning. Your body produces and consumes ketones regularly, so this number will change accordingly. Fat-adaption, after all, is the body's way of getting used to running on ketones, not glucose. Eventually, your body will optimize the level of ketones used, making that reading itself non-indicative of how much fat you will burn.
Acetone and Fat Loss
One popular study circulating among the low-carb community shows a correlation between fat loss and acetone levels, just one of the ketones you can measure. This study, however, did not take the keto diet's benefits completely into account. Instead, it compared a low-fat, high-carb diet to a high-fat, low-carb diet, comparing the effects between the two. Since low-carb diets outperform their counterparts (2), using a high-carb diet for comparison doesn't offer too much information. Instead, studies would need to be conducted on the level of carbs restricted, rather than just a low-carb diet in itself. Since different dieters will have different ketone levels, especially once they become fat-adapted, and since levels of carbohydrates can be either increased or decreased, carb level and ketone level correlations would reveal the truth behind ketones and maximum fat loss. Ketone levels themselves, however, do not.
Because conclusive proof does not exist, ketone levels and fat loss aren't directly linked. While studies do show a correlation, comparing two different diets doesn't reveal actual carb limits, and correlation does not equal causation. High ketone levels over 3mmol/l are used for therapeutic benefits (3), not fat loss, and they may actually slow it down. Once ketone levels reach a high limit, they block the release of the cell's fatty acids. This is great news for those seeking therapeutic goals, such as improving their diabetes or epilepsy symptoms, but it's too high for those seeking other goals.
When Ketone Levels Do Matter
Ketone levels vary based on individualized goals (4). Optimal readings will not be the same for everyone. Non-therapeutic dieters achieve ketosis at 0.5 mmol/l to 1.5 mmol/l, and reach optimal ketosis somewhere between 1.5 mmol/l and 3 mmol/l. These are the readings you should be aiming for, and once you adjust to ketosis, you'll know where your ideal reading lies. If fat-burning is your goal, however, the ketone reading itself isn't the determining factor. Truthfully, it doesn't make any difference. For fat loss, the body needs to remain in calorie deficit while continuously burning fat, so that you're staying in a healthy state of ketosis.
The ketone reading, however, can vary within that 1.5 mmol/l and 3/mmol/l range. Once you reach optimal ketosis, you'll achieve increased satiety—your body will feel more full, you'll eat less, and you'll burn more body fat for fuel (5). This doesn't depend on a specific ketone reading itself, but whether or not you're maintaining a low-carb lifestyle, staying in ketosis, and regularly burning fat for energy. Ideal ketone level readings will differ, so don't take the number too seriously.
Since ketone levels can vary significantly between individuals and their unique goals, they're not the most important part of living a low-carb lifestyle. They don't determine increased fat loss, and for many dieters, that's not a goal at all. Regardless of goals, however, keep in mind that measuring ketones tracks the amount available in your body's fuel tank, not the amount that you're actually using for energy. Completing a high-endurance workout and then re-measuring ketone levels could see a drastic change in numbers, even though you're successfully fat-adapted. For those just starting out, readings will naturally be lower as they adjust to running off fat, but that doesn't mean they're not burning it effectively. Ketone levels simply can't track this.
Overall, staying within a healthy range for your goals is key, but a specific ketone reading isn't necessary. Many long-term keto dieters will measure only sporadically, as they know what to eat to stay on track. Don't rely too much on numbers, as they can only tell you so much.
1. Smith, R.N., Mann, N.J., Braue, A., Mäkeläinen, H. & Varigos, G.A. (2007) A low-glycemic-load diet improves symptoms in acne vulgaris patients: a randomized controlled trial. The American Journal of Clinical Nutrition, 86, 107–115. https://www.ncbi.nlm.nih.gov/pubmed/17616769.
(2) Westman, Eric C., et al. “Low-Carbohydrate Nutrition and Metabolism.” The American Journal of Clinical Nutrition, vol. 86, no. 2, Aug. 2007, pp. 276–84. https://academic.oup.com/ajcn/article/86/2/276/4633078.
(3) Veech, R.L. (2004) The therapeutic implications of ketone bodies: the effects of ketone bodies in pathological conditions: ketosis, ketogenic diet, redox states, insulin resistance, and mitochondrial metabolism. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 70, 309–319. https://www.ncbi.nlm.nih.gov/pubmed/14769489.
(4) Kennedy, A.R., Pissios, P., Otu, H., Roberson, R., Xue, B., Asakura, K., et al. (2007) A high-fat, ketogenic diet induces a unique metabolic state in mice. American Journal of Physiology. Endocrinology and Metabolism, 292, E1724-1739. https://www.ncbi.nlm.nih.gov/pubmed/17299079.
(5) Boden, G., Sargrad, K., Homko, C., Mozzoli, M. & Stein, T.P. (2005) Effect of a Low-Carbohydrate Diet on Appetite, Blood Glucose Levels, and Insulin Resistance in Obese Patients with Type 2 Diabetes. Annals of Internal Medicine, 142, 403. https://www.ncbi.nlm.nih.gov/pubmed/15767618.