I'm feeling weak and fainting after 20 hours of fasting - what do I do?

Realize this: you’re going from glucose metabolism to running on ketones and fatty acids, which takes time. And it will take a lot longer if you already have diabetes or insulin resistance. It could take months.

Let’s say you’re at two meals. Your first meal is at 2pm and your second at 6pm, then you fast for twenty hours. If you’re having a hard time with this schedule, and you feel weak and faint, back up a little to eighteen hours of fasting. Eat at 12pm and 6pm. You haven’t given your body enough time to adapt. You want to let how you feel dictate how quickly you should go from, say, thirteen hours or so of fasting, eating three meals per day at 7am, 12pm, and 6pm. If you feel good, then go to eighteen, and then when you feel good, to twenty.

When you’re at three meals per day, avoid snacks and add more fat to your meals until you’re comfortable and your cravings go away. You also want to feel energetic and have good cognitive function.

Fainting and feeling weak could be low sodium. Make sure you’re consuming at least one teaspoon of sea salt per day. If you’re exercising you may need a teaspoon and a half. You may also need to increase your B vitamins, especially B1, as well as your electrolytes: potassium and magnesium. Your B vitamins and electrolytes are involved in your metabolism, which helps you to make energy so if you're not taking them that could be why you feel weak and faint. You can add MCT oil to your diet, which gives you more ketones to run on.

You may not be able to get into ketosis without some help if your insulin resistance is severe enough. Other people are using my fasting tea, which seems to help because it has certain phytonutrients to help their blood sugar.

The main point is to reduce your fasting window if you’re feeling weak and faint after twenty hours of intermittent fasting then gradually increase it.