If the sadness is related to keto, it could be simply from the stress of changing what you eat. Or it could even have something to do with the effect on your hormones resulting from cutting back on the glucose intake (also known as carbohydrate ). This is good, because a high-carb diet raises our insulin considerably, and insulin interferes with many of the other hormones. Once it drops, the other hormones need time to figure out what they are doing again.
Please note that women often find that, since their hormones get re-regulated by the new way of eating, weight loss can wait a month or two to get started. If, like a lot of people, you are embarking on this way of eating in order to shed some excess fat, don’t be upset if you don’t drop poundage or kilogrammage right away. It will happen when the time is right. In the meantime, eat.
As long as you are restricting your carbohydrate intake, you can safely eat as much food as it takes to satisfy your hunger. The “eat less, move more” advice is not nearly as important as it is for us to avoid foods that go straight to our hips (sugar, pasta and other grains, starches, etc.). And remember, on a ketogenic diet we eat to satisfy our hunger, not to shove as much food as possible down our gullet. Since fat has over twice the calories per gram as carbohydrate, it takes a lot less fat to give us the same number of calories as the carbs we used to eat.
Keep up your salt intake, and drink plenty of fluids; that will help, too.