BLUF: Many questions must be answered before the military considers recommending ketogenic diets to improve performance. However, a growing body of evidence supports KD for managing obesity, diabetes, and epilepsy.
What is a ketogenic diet?
A ketogenic diet (KD) promotes ketone body production, with the goal of mimicking a fasting state and shifting the primary energy source from carbohydrates to fat. Ketone bodies, or ketones, are molecules made by the liver from dietary fat and can be used as an energy source. Nutritional (physiological) ketosis is defined as a blood ketone body concentration of 0.5 to 5 mM (millimolars). Within about 5 days of eating a high-fat (70–80%) diet, your metabolism will shift from burning carbohydrates to burning fats and ketones.
The ketogenic diet has been recognized as a treatment for epilepsy for centuries. It came to the forefront in the 1980s when the U.S. military examined it as a possible approach for optimizing performance. The hypothesis was that relying more on fat than carbs for energy might improve performance during the low-intensity and long-duration demands of many military missions, while saving carbohydrate stores for high-intensity activities. This shift could be beneficial by tapping into the most dense energy source: fat stores. At that time, nothing really came of the KD because the results were insufficiently conclusive and opportunities for more research became limited.
Today, popularity of the KD continues to grow. In addition to helping control epileptic seizures, KD appears to be an effective dietary plan for weight loss, diabetes, metabolic syndrome, and more recently, Alzheimer's and Parkinson's Disease. Keto diet strategies clearly serve a role in short-term and possibly long-term improvement in various metabolic systems and potentially neurological disorders. However, responses to such diets vary because one person’s ability to restrict carbohydrates long-term often differs from another’s.
What is the nutritional breakdown of a ketogenic diet?
Ketogenic diets can range between ratios of ketone producing (fat) and non-ketone producing nutrients (carbohydrates and protein) from 3:1 to 4:1. The graph compares the macronutrient distribution for KD and the standard American Diet (AD).
The table below shows the range of percent of calories (kcal) and the grams from each macronutrient for a 2,000-calorie KD and AD diet. Importantly, a ketogenic diet essentially eliminates grains, legumes, many vegetables, most fruits, and some dairy (mainly milk and low-fat) products.
Consuming a strict KD for 5 days will result in nutritional ketosis, where ketones build up in your blood and urine. However, it might take longer to adapt so you feel good. These ketones provide the fuel needed for daily living and exercise. Since the body stores far more fat than carbohydrates, some people think being in a state of ketosis provides an almost “endless” supply of energy (from fat). This is true, unless you engage in high-intensity exercise, which requires carbs as fuel. Importantly, you don’t need to be in ketosis to use body-fat stores, so energy will be available regardless of whether you’re in ketosis or not. You use more fats than carbs as fuel for most daily activities as well as for low- to moderate-intensity exercise. The real question is whether KD can improve performance.
Sample keto meal plan for one day
Scrambled eggs (2 eggs + 1 oz butter)
327 calories, 1 g net carbs, 31 g fat, and 11 g protein
Cheese roll-up (2 oz cheddar cheese + ½ oz butter)
331 calories, 2 g net carbs, 30 g fat, and 13 g protein
Asian beef salad (1/3 lb ribeye on 1.5 oz lettuce + 1.5 oz cherry tomatoes + 1 oz cucumber + ¼ red onion with sesame mayo)
1,024 calories, 7 g net carbs, 96 g fat, and 33 g protein
Celery and cream cheese with herbs (2 oz cream cheese + ½ tsp olive oil + ¼ garlic clove + fresh parsley + lemon zest with 1 celery stalk)
230 calories, 4 g net carbs, 22 g fat, and 4 g protein
Pesto chicken casserole (6 oz chicken made with ½ Tbsp butter + 1¼ Tbsp pesto + 1/3 cup heavy whipping cream + ¾ oz olives + 1¼ oz feta + ¼ garlic clove on 1¼ oz leafy greens with 1 Tbsp olive oil)
1,018 calories, 6 g net carbs, 93 g fat, and 38 g protein
2,930 calories made up of 20 g net carbs, 272 g fat, and 99 g protein
*net carbs = total carbs – fiber (g)
Can a ketogenic diet improve my performance?
Even though KD increases the ability to burn fat, the scientific literature hasn’t consistently demonstrated it as superior to current sports nutrition guidelines for improving performance.
Overall, the science is mixed about the effects of KD on endurance performance. Also, the performance benefits observed have been among athletes and might not be relevant for the military. For example, a 2-second improvement in a 2,000 meter row or a 2% improvement in cycling distance in 30 minutes don’t translate to a military mission, especially given the amount of effort needed to maintain KD in a field setting. Also, for most dietary interventions, there are typically high-, low-, and non-“responders,” so it’s important to find which type of diet best fits your lifestyle, performance goals, and personal metabolic profile (percent body fat, muscle fiber type).
If you’re participating in high-intensity exercise, such as sprinting, KD could compromise your performance because your ability to use carbohydrates as fuel will be impaired. Since carbs are required for high-intensity activities, KD is not the preferred diet.
Because KDs are hard to sustain, ketone supplements have been introduced to the marketplace. For information about these, you can read the Operation Supplement Safety (OPSS) article about ketone supplements.
What are the potential side effects of following KD?
Short-term side effects of KD can include nausea, thirst, headache, dizziness, fatigue, and increased urination. These side effects should subside once your body has “adapted,” but it isn’t clear how long that takes (usually 1–4 weeks). Also, any increase in carbohydrate intake will disrupt ketosis, and side effects can recur if you don’t strictly adhere to your KD. In other words, there are no “cheat meals” when you’re on a ketogenic diet. Continued consumption of KD can result in constipation, electrolyte imbalances, and/or other nutrient deficiencies/insufficiencies, unless appropriately accounted for.
One other concern is that KD might lack many nutrients that benefit gut microbes (phytonutrients, fiber), and include several compounds that could adversely affect the gut microbiota (short-chain fatty acids, artificial sweeteners), but this is an emerging area and the relevance to health and performance is unclear.
To date, the research to support KD or KS for enhancing the performance or health of any military community is insufficient. Service Members should leverage the expertise of their unit dietitians to develop individualized nutritional strategies and engage with their human performance team to optimize all aspects of performance. The military will continue to follow the nutrition regulations published by DoD: “Army Regulation 40–25, OPNAVINST 10110.1/MCO 10110.49, and AFI 44–141: Nutrition and Menu Standards for Human Performance Optimization.” The regulation is based on the most up-to-date science and forms the foundational nutritional strategies for our Service Members. However, the evidence for KD promoting a better body composition and mitigating diabetes is quite compelling. Ultimately a Service Member’s specific health goals and successful performance of mission-essential tasks should drive their diet choices.