Cutting down on carbs takes a lot of adjustment, and if you’ve gone very low carb (<50g/day), you've probably dropped into ketosis. Some people are fine with it, but others develop a glucose deficiency as a result of poor metabolism or liver function, and candida can feed on ketones, so there's no benefit to it. If you eat about 60g of carbs a day you can stay out of ketosis, and provide enough glucose for your brain and muscles to function. The rest of your cells will happily run on fat, which is where you should get the rest of your calories (after adequate protein intake). By the way, you should introduce your friend to the magic of gluconeogenesis, or maybe remind him people don't die while fasting.