Most people follow diets for improved:
The ketogenic diet is a very low-carbohydrate diet (i.e., <50 grams a day) where the body burns fat instead of glucose for energy and produces ketones. Going “keto” has resurfaced as a popular way to achieve all of these goals: improved body composition, health, and performance. With any diet, however, it is important to understand whether the claims are relevant to you.
Improved Body Composition
You definitely can lose weight on a ketogenic diet. But, you can lose weight on any diet where you eat less than you need. Quantity matters: if you eat too much, you will gain weight.
The reason why many people lose weight on keto diets, however, is that they reduce their overall intake inadvertently. Keto diets have complete elimination of items that people routinely overeat (i.e., carbs), and fat is filling. The result? Less total food is (often) consumed. The weight loss is not because you have become “fat-adapted.” You become “fat-adapted” because you are eating more fat than carbs (you burn what you eat), but it is the overall quantity that determines weight loss.
The ketogenic diet has been used as a therapeutic intervention for epilepsy (3). It also has been suggested as a treatment or adjuvant for some cancers, but human research is inconclusive (4). Regardless, therapeutic interventions do not necessarily translate to general health guidelines.
Another potential health benefit from ketogenic diets is “metabolic flexibility”: the ability to burn fat or to burn carbohydrate (5). Metabolic inflexibility, the opposite, means the individual requires a static fuel source and is associated with various diseases such as diabetes, heart disease, and polycystic ovarian syndrome (5). By passing through periods of only eating fat (or just not eating), the body becomes more efficient at burning fat. Conversely, when one eats carbs, one becomes more efficient at burning carbs. Metabolic flexibility is a benefit from periods of ketosis. However, a ketogenic diet may not outperform just skipping breakfast periodically (a la intermittent fasting) and not chronic overeating in terms of becoming more metabolically flexible.
One of the potential drawbacks regarding a long-term ketogenic diet is damage to the diversity of your microbiota. The microbiota in the gut is an important part of the immune system (and therefore your health), yet we do not yet know the relevance of each species with regards to health (6). Low carbohydrate diets reduce species diversity due to the lack of plant fiber (i.e., food for the microbiota) (7,8,9,10). This has potential unknown long-term consequences for which we do not yet know its significance.
There is research that suggests elite ultra-endurance runners may achieve better performance using a ketogenic diet (Volek et al., 2016). Most athletes are not elite, but more so, do not participate in ultra-endurance endeavors. Ultra-endurance efforts occur at sub-maximal intensities (e.g., 70% of VO2 max) (11). Conversely, Pepperdine University did a metabolic analysis of top CrossFit athletes in 2012; the athletes relied almost entirely on carbohydrates during their workouts (12). High to maximum intensity efforts require carbohydrates. This is why the perhaps “boring” split of 40% carb, 30% protein, and 30% fat of one’s caloric needs can be so effective: it provides enough carbohydrates for high-intensity exercise (especially for the once-a-day-workout population), enough protein for lean mass, and enough fat to sustain energy between sessions (among other functions).
It is possible that the above-listed considerations are at odds with each other. Perhaps you have found you lose weight more easily on a ketogenic diet compared to others, yet you feel sluggish during workouts. You then must prioritize your goals: do you want to lose weight or do you want to perform better? Perhaps you decide to use a ketogenic diet temporarily to achieve certain goals. However, for many, it is possible (and likely more enjoyable!) to improve body composition, health, and performance on more moderate macronutrient ratios.
About the Author
EC Synkowski is a candidate for an MS in Human Nutrition and Functional Medicine anticipated in December 2017. EC is a Certified CrossFit Level 4 (CF-L4) Coach, worked as an Instructor and Flowmaster on the CrossFit, Inc., seminar team for more than 10 years, currently coaches at CrossFit Roots in Boulder, CO, and blogs at OptimizeMeNutrition.com.