It may be more challenging to exercise
On the keto diet, it may be challenging to exercise, says Jackie Newgent, R.D.N., C.D.N., nutritionist, chef, and author of The Plant-Based Diabetes Cookbook. On the diet, you severely restrict your intake of carbs, which are your body’s main source of energy. This can negatively affect physical performance and energy levels—which in turn can make it really difficult to get active, especially at the start of the diet.
Some research has shown that increased levels of ketones in the blood could increase feelings of fatigue and decrease the desire to exercise, too.
You may put more stress on your kidneys
The kidneys play an important role in metabolizing protein, and it’s possible that eating too much of the nutrient can have a negative impact on kidney function. While ketogenic diets are supposed to be much higher in fat than they are in protein, many keto eaters make the mistake of loading up on lots of meat, Mancinelli says. The result? You could end up eating way more protein than you actually need.
Here’s the tricky part: There’s no definitive answer for how much protein you’d have to eat before you run into trouble. “It really depends on how much protein a person is consuming versus how much they need, as well as the health of their kidneys at baseline,” Hultin says. That’s why it can be helpful to speak with a nutritionist or doctor who can help you tailor your diet before going keto.