If there’s a diet trend you’ve heard buzzing around the most this year, it’s probably this one. A typical keto diet consists of roughly 60 to 80 percent fat, 20 to 25 percent protein, and 5 to 10 percent carbs. By consuming such a high intake of fats, you’re trying to induce ketosis, which is when your body has gone through its source of carbs and starts burning fat instead. Your body produces ketones and uses them as sources of energy for your brain and central nervous system.
A couple of pros to this diet are the high percentage of protein and, like paleo, the concentration on whole foods. The cons are the high percentage of fat and insufficient amount of carbs. There’s a reason why many endurance athletes lean on simple sugars, such as gummies or GUs, during long rides—they provide energy in the form of carbs that break down quickly. Fats, on the other hand, take a lot longer to digest.
“It’s very inefficient,” Rizzo says. “It takes a lot more work for the body to break down fat and use it as fuel. You’re almost putting more work on your body than you need to because you’re just not storing as much carbs in the muscle and the liver, which is known as glycogen.”
Generally speaking, you’re not getting a lot of vitamins, minerals, fiber, or antioxidants, Rizzo says. “That can lead to deficiencies in basic nutrients such as vitamin C or A—things that should be part of any person’s diet.”
These are nutrients you not only need for your everyday life, but also fuel you need in training—especially for the last leg of a ride or race when you need to finish strong. In those anaerobic exercises, your body can’t actually burn fat because oxygen has to be present in order to do that. Therefore, fat can’t give you proper fuel to help propel you across the finish line as fast as you want during a hard and fast effort.
“For people who might be trying to get faster or PR in a race, it’s going to be a rough day for you, because your body was running on a fuel source that it wasn’t really designed to,” says Amy Goodson, M.S., R.D., C.S.S.D., a dietitian in the Dallas-Fort Worth area.
If you’re already fat-adapted and prefer to simply ride your bike at a mellow, steady state for yours, then a keto diet might work well for you. But if you plan on any HIIT workouts, charging up hills during rides, or sprinting for town lines or finish lines, then you want to avoid.
The Verdict: If you’ve got big goals for the bike in 2020, then keto is not for you—you just won’t make it. The diet lacks carbs and fiber, thus depriving you of required nutrients, energy, and mental sharpness you need to ride your best.