2. A vitamin or nutrient deficiency
According to the Cleveland Clinic, a vitamin deficiency, such as a lack of vitamin D or vitamin B12, could cause you to feel very tired. Dehydration can have the same effect.
You might also suddenly feel exhausted if you’ve recently started a high-protein diet. It’s not the protein itself that makes you tired, but the lack of carbohydrates. According to the Mayo Clinic, severely restricting carbs causes your body to enter ketosis, where it breaks down fat for energy. Side effects of ketosis (sometimes called “keto flu”) include fatigue, dizziness, weakness, and “brain fog,” among others, according to one study.
These side effects are usually temporary. But if ketosis is the cause of your sudden drop in energy, you may want to add more complex, fiber-rich carbohydrates to your diet. These include fruits, vegetables, and whole grains like oatmeal and brown rice. The Dietary Guidelines for Americans recommend that carbohydrates make up 45 to 65 percent of your total daily calories.
Likewise, skipping meals or following a very low-calorie diet could sap your energy. Women should try to avoid consuming fewer than 1,200 calories per day, and men should avoid consuming fewer than 1,500 calories per day, according to Harvard Health Publishing.
But keep in mind that these are minimums. The Dietary Guidelines for Americans recommend that adult women consume between 1,600 and 2,400 calories per day, and men consume between 2,000 and 3,000 calories per day, depending on age and activity level. Check the Estimated Calorie Needs Guidelines chart or use a calorie counting app.
