Sports nutrition has evolved in quantum leaps in the last decade, with entire changes in methodology that can be especially valuable to climbers. A strategy that typifies the modern approach is the ketogenic diet, which trains your body to burn ketones derived from fatty acids, rather than glucose from carbohydrates, as your main energy supply.

While individuals respond differently to various plans, the ketogenic diet has worked for me. I became aware of it four years ago when trying to shed a few pounds to nail a project at Pembroke in the U.K. I had dabbled with low-fat, semi-starvation diets two decades previously and vowed never to return. However, I consulted a nutritionist friend, Glen Burrows, who outlined a strategy he claimed would help me lose weight without feeling hungry, deliver continuous energy and improve recovery.

I was skeptical, but followed some of Glen’s advice, lost weight and sent the route without suffering. Still, the experience was hardly life-changing—until I abandoned the diet and my climbing level crept back down. This year I followed the ketogenic diet to the letter and sent the hardest route I’ve ever climbed, a new line at Kilnsey. I owe success to the diet, because nothing else in my lifestyle changed, yet my climbing just kept spiraling upward. Furthermore, my outlook toward food improved, and I now genuinely enjoy eating in a new, healthier way that I used to view as punishment.

The main principle of the ketogenic diet is to avoid simple sugars and complex carbs with a high glycemic index (GI), keeping even low-GI carbs to a strategic minimum while seeking energy from high-quality fats. This diet is believed to maintain low, constant insulin levels, promoting fat burning and reducing the hunger pangs that typically follow carbohydrate consumption. For those familiar with the paleo strategy, the ketogenic diet is essentially a tweaked version. An additional component of the diet is to avoid items such as dairy, wheat and processed foods that can strain the digestive system and initiate an inflammatory response. Many people feel they recover faster from training when avoiding these foods. A few other foods such as lentils may cause minor inflammation.

To try a ketogenic program, cut out anything sugary: No cakes, sweets, chocolate or alcohol. Minimize fruit. The big complex carb to avoid is wheat—pasta and bread are out. Avoid or minimize rice, and eat white potato only when cold after being cooked, to lower the GI. The “magic” carbs are sweet potatoes and quinoa, which have a low GI, but consume even these moderately. Go for healthy omega-rich fatty foods such as avocado, oily fish, nuts and olive oil. If you ditch dairy, nut butter is an alternative to cheese, and almond or oat milk can replace regular milk. There is even a special ketogenic coffee (blended with unsalted butter and coconut oil) to kick-start you into ketosis, or fat-burning, in the morning.

Classic ketogenic meals are meat or fish with a pile of green vegetables for micronutrients, or a “superfood” salad based around nuts, avocado and mackerel. Eggs are key for breakfast, especially combined with fish, spinach or avocado. You’ll feel less hungry eating them this way than with toast. At lunchtime also aim for low or no carbs to maintain the state of fat metabolism (even two ounces of sweet potato may take you out of ketosis).

Evenings are the time to ingest carbohydrates since they spike production of insulin, a potent anabolic hormone necessary for muscle repair. Eat a small serving of the above magic carbs, and your body should release only enough insulin to promote the beneficial metabolic processes.

A note of caution: It is possible to consume too much protein, leading to gluconeogenesis or the conversion of amino acids to glucose. This contradicts the aim of a ketogenic diet, which is to keep glucose levels low and encourage the production of ketone bodies. Consuming the good carbohydrates in moderation should keep you on track.

Many climbers will adopt a more relaxed version of the ketogenic diet during the training season and tighten up for climbing or competing season. However, even if you drift back to more carbs and fewer fats, to promote recovery you should still avoid foods that cause high inflammation.

If you’re keen to try it, the hardest parts of switching to a ketogenic diet are ditching sweets and eliminating foods that have been staples our entire lives: I took sandwiches to the crags for 30 years. But you soon stop craving them and start to really taste and enjoy the alternative foods. At first the strategy seems counterintuitive, seeing as for years we believed that fat was the enemy, but we now know that the real enemy is sugar.

For more information, read Low Carbohydrate Performance by Jeff Volek, and listen to podcasts from Ben Greenfield, Tim Ferriss and Dr. Peter Attia. And always check with your doctor before beginning any new diet.

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