The worst thing you can do on a low carb diet, is to eat too many calories. I’ve seen way too many patients in perfect ketosis all week, lose no weight, because they are eating too much. If you are eating much over 1500 calories a day, you probably aren’t going to lose weight fast enough to put up with low carb deprivation. The worst thing you can do if you want to lose weight on a low fat diet, is eat too much sugar. You will be hungrier and crankier on a low fat diet, and eating too much sugar will make mood swings, depression and cravings worse.