That’s not to say everyone starting out on a keto diet ends up wholly incapacitated for days. “You might find that you fatigue more quickly or that exercise seems harder than normal,” says Seattle-based nutritionist and Academy of Nutrition and Dietetics spokesperson Ginger Hultin, MS, RDN. Your body might also have an easier time transitioning (read: fewer symptoms) if you were already eating a relatively low-carb diet, Mancinelli explains.
Keto flu is an unofficial way to describe how many people feel shortly after starting a ketogenic diet, and it can include both physical and emotional symptom—like nausea, cramping, lack of energy, and irritability, to name a few. It’s what happens when the body and the brain are forced to adjust to a sudden carbohydrate deficiency, says Abbey Sharp, RD, a Toronto-based nutritionist and blogger at Abbey's Kitchen.
Another mineral you may want to supplement is potassium. While there is no concrete evidence that a dramatic potassium loss occurs on a low-carb regimen, Sondike says to ensure against problems he recommends patients use Morton's Light Salt -- a potassium chloride product that he says can add back any of this important mineral that's lost. Eating a few almonds is also a good way to supplement this mineral without adding carbs to your diet.
If you’ve decided to move forward in trying the keto diet, you will want to stick to the parameters of the eating plan. Roughly 60 to 80 percent of your calories will come from fats. That means you’ll eat meats, fats, and oils, and a very limited amount of nonstarchy vegetables, she says. (This is different from a traditional low-carb diet, as even fewer carbs are allowed on the keto diet.)
Although many people find that their energy and stamina improve on a keto lifestyle, trying to do too much in the early stages can worsen keto flu symptoms. Well-known ketogenic researcher Dr. Steve Phinney has conducted studies in endurance athletes as well as obese individuals demonstrating that physical performance decreases during the first week of very-low-carb eating. Fortunately, his research also shows that by week 4, people typically perform better than before they started keto.
Still, it can be hard to get enough fat when you first start this diet. Butter, nuts, coconut and olive oils, and fatty cuts of meat are all on the menu. However, don't go overboard with polyunsaturated fats like soybean, corn, or sunflower oil. Keto dieters who increase their intake of those fats often end up with gastrointestinal distress that causes them to jump ship.
What can you drink on a ketogenic diet? Water is the perfect drink, and coffee or tea are fine too. Ideally, use no sweeteners, especially sugar. A splash of milk or cream in your coffee or tea is OK, but beware that the carbs can add up if you drink multiple cups in a day (and definitely avoid caffe lattes!). The occasional glass of wine is fine too.