A low-carb diet might reduce your hormone production, specifically your main thyroid hormone (T3), which regulates your metabolic rate. A low-carb diet can also lead to lowered testosterone and elevated cortisol in men, all of which lead to less energy, slowed metabolism, low sex drive, and impaired immune function, Gorski says.
You might feel more energized — or more lethargic.
This depends on where you’re starting. Cipullo explains: “Energy levels vary depending on whether someone was with excess storage on their body versus with adequate or inadequate stores of glycogen and fat. If someone was with excess fat storage, they will likely feel increased energy while someone with too little reserves will feel worse following such a strict diet.”
On the flip side, you could be the kind of person who becomes more lethargic. While some people can function better after they’ve gotten used to the low-carb lifestyle, it doesn’t work well for a majority. “It can be especially hard for very active people, as they tend to need more carbohydrates to fuel workouts/training,” Gorski says. All three of our experts agree that healthy forms of carbs like beans, lentils, starchy vegetables, and whole grains and proper hydration are the way to go for high and sustained levels of energy.