A clinical version of the keto diet has been used for decades as part of the treatment pediatric epilepsy and cancer. And modified versions have gained popularity lately in popular culture for weight loss. Advocates of the diet herald it as a miracle cure for obesity and other lifestyle diseases. They also claim it improves athletic performance and mental clarity for healthy adults. But some researchers caution that the modified keto is relatively high in saturated fat, which has known cardiovascular risks. Muscles get most of their energy from glucose to fuel intense bouts of exercise. This causes some concerns keto could negatively affect athletic performance. So what happens when we look past the sensational media posts? Today we’re going to review the science regarding both athletic performance and general health.
What is Keto?
A diet is simply what a person eats daily. (Check out our post on nutrition basics here!) The typical Western diet contains a ratio around 40:30:30 for carbohydrates, protein, and fat. Various organs of the human body prefer glucose derived from carbohydrates as fuel. We eventually run out of glucose when this balance is skewed towards higher fat. Your body makes endogenous ketone bodies to be used for fuel if you eat fewer than 20 grams of carbohydrates each day. This person is considered to be in ketosis, which is how you get the name ketogenic diet.
Clinical vs Modified Keto
There are two versions of keto. Clinical keto is what doctors or dieticians prescribe in a clinical setting. Patients have blood drawn daily to confirm the state of ketosis. Hospital registered dietitians make personal dietary plans for each patient. They have to make sure both carbohydrate and protein intake is low enough to prevent the body from making glucose. The diet is highly unpalatable, as fat sources are from unsaturated fats.
Modified keto is a newer phenomenon that serves as a catch-all phrase for trademarked diets, such as the Adkins Diet, or any diet where fewer than 60 grams of carbohydrates are consumed daily. It has gained popularity as recent studies have found a connection between diets high in processed sugars to contribute to metabolic syndrome, which increases the risk of heart attack, stroke, diabetes, and other health concerns. Many of these diets do not place an emphasis on consuming unsaturated over saturated fats, which has been shown to reduce the risk of heart attack, stroke, or other cardiac events up to 17%.
Weight Loss and Keto
Kosinski & Jornayvaz (2017) looked into to how keto could change risk of cardiac event in an obese or otherwise health-compromised patient population. Studies regarding keto and its effects on obesity management are overall positive for short-term weight loss. Patients were able to lose body fat much faster than their controlled counterparts for study durations lasting fewer than 12 weeks. Seidelman, et al. (2018) has some concerns for chronic adherence to a high-fat diet, however. In a massive study spanning nearly three decades, they found an increase in mortality rate or near-term mortality incident, such as massive heart attack or stroke, in patients who ate 70% or more of their calories from fat. This number was more dramatic with patients who chose saturated fat sources instead of those from vegetable or nut sources.
Moderation Is Important
Seidelman, et. al. (2018) found the groups that consumed moderate carbohydrates, 45-55% of their daily calorie intake, lived the longest. They do not recommend keto as a long-term diet. Kosinski & Jornayvaz (2017) found improvements in total cholesterol and a decrease in LDL amounts, which is considered “bad” cholesterol, when morbidly obese patients participated in a six- to 12-week modified keto. They recommend use of keto in short durations for patients whose lifestyle disease already puts them at an increased risk for near-term mortality events more so than the risks associated with increasing their fat intake.
Exercise and Keto
The athletic population usually have different dietary goals than morbidly obese patients. They may want to lose some body fat, but they will also want to build or maintain muscle mass while fueling physical performance. When evaluating the effects of a modified keto and athletic performance, several studies concluded that keto reduced body fat percentages upwards of 12% in a six- to 12-week time frame. This was consistent even when the participants were consuming more calories than they expended on a daily basis. Under normal conditions, this would typically cause an increase in body fat percentage.
However, while body fat decreased, lean body mass either showed no change or actually dropped. Athletes also saw a negative impact in cholesterol levels throughout the studies. There was a 5% increase in total cholesterol and a 10% increase in LDL levels, placing them at a higher cardiovascular risk than they started during the course of the study.
Keto Can Decrease Athletic Performance
Kephart et al. (2018) found athletes who participated in longer duration and lower intensity workouts reported no major changes in athletic performance when adhering to modified KD. However, they echoed other’s concerns for increased cardiovascular risk factors, as their participants had a 35% increase in LDL levels. Performance did change with athletes who participate in resistance training and high-intensity exercises such as powerlifting and HIIT training. Urbain et al. reported a significant decrease in VO2 max and peak power output in their athletes after six weeks using keto compared to their starting values. Zinn, et al. also found their athletes reached exhaustion two minutes sooner when eating a keto diet. These athletes were able to perform low- to moderate- intensity workouts but didn’t have the energy to even attempt high-intensity workouts.
The athletes Zinn et al. followed self-reported better-perceived recovery between workouts, but these were based on post-study interviews rather than actual biometric markers. When studies evaluated biochemical changes associated with recovery, Kephart et al. (2018) found keto interfered with an athlete’s ability to properly metabolize iron. This study was only three weeks long. Athletic performance was not impact during this time. However, keto does decrease blood flow to muscles during and after these workouts. This may indicate a reduction in the muscles’ ability to recover between exercise bouts.
Should You Try Keto?
Research supports short-term use of clinical or modified keto for morbidly obese patients. It can quickly reduce body fat percentages and other problems associated with near-term mortality events. But use caution when using keto as a long-term diet choice. High-fat diets tend to correlate with a decrease in life expectancy. Researchers seem to agree on a sweet spot for keto adherence of six to 12 weeks at a time. After a diet break, you can repeat keto as needed until you reach your desired BMI.
Research does not support its use in a healthy or athletic population, however. Body fat percentages dropped for athletes consuming a hypercaloric keto but they also lost lean muscle mass. Most of us want to keep or gain muscle when exercising, not lose it. Keto can also decrease power and strength output for athletes, and has negative implications for recovery. A moderate carbohydrate diet can conserve muscle mass and improve athletic performance. So adding keeping some small amount of carbs in your diet may be best for athletes trying to improve their power but also lose some body fat.
Keto certainly seems to have its time and place for managing morbid obesity. It’s not a magic bullet for all people, though. If you’re a competitive athlete or very active person and wish to try keto or another very restrictive diet, we highly recommend working with a registered dietician!
Jess Bateman has combined a knowledge of Orthopedics and injury prevention to benefit many athletes in the world of functional fitness and weightlifting. She herself has both competed at a national level in Olympic Weightlifting and spent the last five years coaching Senior and Youth athletes, as well as having obtained a USAW-SPC credential.