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Everything Runners Need to Know About the Keto Diet

We dive deep into the ketogenic diet and how to (or if you should) make it work for you.

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If an exponential increase in Google search rankings, a multitude of innovations on the market, and the rise in prices of related in-demand, high-fat foods are an indication of the diet du jour, then keto is certainly having its day in the sun. Let’s take a look at what the science says about the keto diet for runners.

The ketogenic diet is not a new diet; it’s a high-fat, adequate-protein, very low-carb lifestyle that’s been used for decades to treat epileptic seizures as well as other chronic conditions, such as metabolic syndrome. The premise is this: By severely restricting carbohydrates, the body is forced to either find an alternate source of fuel or perish. Survival mode and evolution kicks in, and instead of being a carb-burning machine, relying on blood sugar for fuel and the pancreas and insulin to utilize said fuel, the body transitions to burning fat stores and dietary fat as the liver creates a source of fuel known as ketones. When this happens, the body enters a metabolic state known as ketosis, in which the body’s energy supply comes from ketone bodies in the blood. This is in direct contrast to the native state of glycolysis, in which blood glucose provides most of the energy.

Here’s How It Works

On your plate, keto looks like high-fat butter-coffee and a cheesy omelet topped with avocado and bacon for breakfast, a lettuce-wrapped burger for lunch, and a ribeye steak topped with sautéed mushrooms and creamed spinach for dinner. In other words, hold the grains, bread, fruit, and craft beer.

Ketogenic diets work for a multitude of reasons: There is both a metabolic shift and a reduction in overall calorie intake at play. Given the severe carb restriction, ketogenic diets do not allow for intake of empty-calorie, high-sugar treats, nor do they allow for an overwhelming choice of foods. Many dieters stick to their plan and rarely surpass calorie goals because their options are limited. What’s the point of butter without popcorn or guac without tortilla chips? In addition, the elimination of carbs ultimately reduces blood sugar fluctuations, decreases appetite, and significantly reduces hunger signals.

Physiologically, the diet is effective because it disrupts the usual state of glycolysis, which is when circulating insulin promotes storage of body fat and blocks the release of fatty acids from adipose tissue. Instead, in a ketogenic state, fat reserves are readily released and consumed as ketone production occurs. These ketone bodies can then be used by the brain and muscle tissue as a fuel source to replace some of the needs originally supplied by glucose. This is why ketosis is sometimes referred to as the body’s “fat-burning” mode.

What Does the Science Say?

The exact definition of a ketogenic diet in terms of carbohydrate prescription may vary slightly, but published studies and texts agree that the diet should be designed around the following principles:

  1. An extremely limited carbohydrate intake: Supplying less than 20 to 50 grams of carbohydrates per day. That’s less than 5 to 10 percent of your total daily calorie intake.
  2. Adequate protein to support lean body needs: Approximately 0.5 to 0.7 grams of protein per pound of lean mass (i.e., you don’t feed the extra weight you hope to shed!). This should total about 20 percent of your total daily calories.
  3. High in fat: Supplying about 75 percent of daily calories. Overall, your daily intake should supply at least two times as much fat compared to every combined gram of protein and carbs. For example, if you consume 10 grams of fat, you would eat no more than 5 grams of a mix of protein and carbs and choose protein first since it’s more ketogenic than carbs.

When it comes to the keto diet for runners, many endurance athletes are practically baptized on bagels and drowning in gels and energy bars. But six-time world Ironman champion Dave Scott has turned to the ketogenic diet as a way to fuel his health and performance. A major shift from his days of being sponsored by sports drinks and bananas, Scott now believes in, personally consumes, and recommends a low-carb, high-fat approach to eating. He has observed that this satiating, steady-energy diet has led to improvements in performance, health parameters, and even body composition. His appetite is reduced as a result of getting his body into a state of ketosis.

Science supports Scott’s opinion: Ketosis regulates two key hormones, ghrelin and leptin, which signal hunger or fullness. When it comes to weight loss and improvements in body composition, multiple research studies have found keto to be effective. One study established that a low-calorie ketogenic diet results in both fast and longer-term weight loss. This study compared effects of a low-calorie ketogenic diet (LCKD) versus a standard low-calorie diet (LCD). The LCKD resulted in significant effects on body weight at 6, 12, and 24 months. At 24 months, the diet brought even greater reductions in body weight, waist circumference, and body-fat mass. In those who completed the program, there were significant effects on weight loss at 2 weeks, 2 months, 4 months, 6 months, 1 year, 1.5 years, and 2 years.

And as for overall health? A study of 46 men compared the effects of two different diets where energy intake and output offset each other: a very high-fat, low-carb diet (73% fat / 17% protein / 10% carbohydrates) versus a low-fat, high-carb diet (30% fat / 17% protein / 53% carbohydrates). Both caloric-restriction diets led to improvements in weight (loss of 12 kg versus 11 kg, respectively), but the keto diet showed more significant total health (circulating metabolic markers) improvements after just 8 weeks, as compared to 12 weeks for other diets. And weight loss on this plan is typically quick; in this study, dieters lost 4.8 kg (10.5 lb.) during the first four weeks. The plan has support from experts like Fredrick J. Stare, professor of nutrition and epidemiology at the renowned Harvard T.H. Chan School of Public Health: “The low-fat diet backfired. American’s obesity epidemic skyrocketed even while our fat intake went down.”

However, not all of the research on the ketogenic diet is positive and not all clinicians advocate for this restrictive approach to eating. While dieters enjoy keto because it allows intakes of some of their favorite foods that they once believed to be forbidden, clinicians criticize the diet for severely restricting or eliminating whole grains, fruit, and other choices, and they question it as a long-term approach to health and wellness. As a registered dietitian, I have seen the positive effects this diet can bring about for weight loss, for quieting sugar cravings and appetite, and for those struggling with chronic diseases. But I’ve also counseled plenty of clients through side effects like dehydration, electrolyte losses, fatigue, micronutrient deficiencies, negative impact on blood lipid levels, and general difficulty with making it work—which may make the keto diet tough for serious runners.

If you want to try keto, know that over the short term, it’s likely a harmless approach to quick weight loss. The clinical trials investigating its long-term safety in general populations are limited at this time, but it appears safe past 36 months. Any research looking beyond three years is concentrated on pediatric, epileptic populations and should not be translated to generally healthy adults. While the ketogenic diet is great for quick weight loss, you’ll want to think twice before you land on it as the be-all, end-all diet for life. While some studies suggest that adherence to a keto diet for up to 36 months far outpaces the acceptance of a low-fat diet, other studies have found that after the first few months of weight loss (three to six months), dieters begin to plateau, and the benefits of keto were similar to those of a low-carb or a 40/30/30 plan over a year’s time.

Should You Try It?

Are you looking for weight loss, less hunger and reduced appetite, and a steady level of energy? Are you willing to put in a few weeks of totally overhauling your diet before adapting to this way of fueling? If you’re looking to lower your sugar intake, want to track your macros, and are willing to say no to your usual way of eating and fueling, then keto could be for you. People who benefit from keto often have significant weight to lose, but advocates of the diet also include individuals looking for better cognition and focus and those looking to improve metabolic markers and levels of inflammation.

The benefits of keto for serious athletes have yet to be fully examined, and current research suggests that keto does not accelerate performance nor is it the right approach for athletes in high-intensity sports. So if you’re looking to PR at your next 10K or if you’re committed to a regimen of HIIT workouts, you might want to rely on good old glucose, which burns easily and without a high oxygen cost, rather than rely on ketones. That being said, many athletes who have transitioned to a ketogenic diet during the off-season and become keto-adapted, consistently relying on ketones for fuel, report performance improvements and finally getting to the elusive race-weight number.

Know Before You Go

Keto is not for everyone, including those with a genetic risk for cardiovascular disease, certain metabolic conditions, and those who find that a high intake of saturated fat drives up their lipid levels. With so many viable choices out there, don’t get frustrated if this is not the diet for you.

For individuals beginning the regimen, it often takes three to five weeks to transition. So don’t wake up on Monday with a plan to start keto when you’ve got an important race on Friday. And don’t give up on keto if you’ve only given it a few days to take hold. Many people following keto respond well to the food choices and guardrails put in place to achieve ketosis, yet others find keto to be too restrictive and eliminating of favorite foods. If you simply can’t survive without fruit or pasta or you’re not a fan of avocado, olive oil, bacon, coconut oil, MCT oil, and heavy cream, then you may want to think twice before diving in.

How to Make Keto Work for You

  • The more strictly you follow this diet, the better. Because it takes days to adapt and burn off the glycogen you have on board, cheat days effectively restart the keto clock, and can also promote inflammation.
  • Set aside a month to strictly follow the keto diet before you consider cyclical approaches or the slightest cheat day, says Robert Santos-Prowse, clinical registered dietitian and author of The Ketogenic Mediterranean Diet and The Cyclical Ketogenic Diet. After that, you can allow yourself “carb breaks”—like integrating some rice or fruit. Fall off the wagon entirely and it will take you a few days to restore ketosis. However, a few breaks here and there can help you to follow this lifestyle long-term.
  • Higher-fat and lower-carb intakes lead to better results. Macronutrient ratios closer to 5 percent of calories from carbs, 20 percent from protein, and 75 percent from fat will lead to higher levels of ketones, and the majority of the weight that is lost stems from fat mass rather than a loss of both fat and lean tissue.
  • Don’t overdo the protein. Excess protein can undergo gluconeogenesis, a process where amino acids are converted to a source of blood glucose, which the body can then rely upon for fuel. To rely on ketones instead, you’ll need to establish a protein intake that’s adequate but not excessive.
  • Hydrate, hydrate, hydrate! The initial weight loss on this diet is due to diuresis or fluid loss. Dr. Carolyn Dean, a medical advisory board member of the Nutritional Magnesium Association, warns followers to hydrate and replace electrolytes or else suffer through dehydration and the effects that accompany it: headaches, fatigue, and feeling like you’ve got the keto flu. Dr. Dean recommends drinking half your body weight (in pounds) in ounces of water. Add ¼ teaspoon of sea salt or mineral-rich Himalayan salt to every quart of drinking water along with a teaspoon of magnesium citrate powder.
  • Plan ahead. You’re probably not accustomed to filling up on fat, so you’ll need to plan ahead to have the right foods available when hunger hits.

Adapted from Sweat. Eat. Repeat. by Pamela Nisevich Bede with permission of VeloPress.

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