While much of the Paleo world is directed toward weight loss, there are a few of us who are looking to it as a hope for help from gut dybiosis and other illnesses that have caused us to lose weight. Thus, we are looking for healthy weight gain, recovery from malnourishment, and intestinal health (i.e, no yeast infections, bacterial overgrowth, etc.). We have all heard testimonies of colon-health recovery via the paleo-world.

Yet, for someone of extremely, extremely low body-weight, the low-carb can present a concern. Yet, there are certain aspects that make a lot of sense to go low-carb, ie., the reduction of inflammation, starches/sugars feeding infections, anti-body attack against starches/grains, etc.

My general question is—what would you suggest for healthy weight gain for those of us with extremely low body weight?

What is a good macronutrient ratio? I.e., I have heard a 50% fat, 30% carb, and 20% protein; or a 60-20-20 or a 40-30-30 respectively ratio. Is there one that is better to gain weight?

More specific questions that pertain to us all follow:
The paleo-world talks about the body being able to make all its glucose needs from fats and proteins. What about someone who has no body fat to lose? Will it all come from the fat consumption in the diet without endangering further loss of body fat or eating muscles? I.e., I have heard that 100g of glucose forming carbs will raise insulin sufficient to shut down ketone production --is ketone production bad or good for a person trying to gain weight? Or something that may potentially bring health to the intestinal system?

If one was trying to eliminate sugars that feed bacteria, yet ensure enough calories and weight gain, should “safe” starches be included (white potatoes, taro, yucca, sweet potatoes, squash, white rice)? Or should a greater number of sugary vegetables (beets, carrots, tomatoes, squash) be included? Is one type better than another then, i.e. if a carrot has glucose is it better than a glucose molecule from a starch?

Related, will a cup of salsa that has a lot of the sugary vegetables (onions and tomatoes) raise blood sugar just as much as one of the maligned starches, i.e., potato?

Is the sugar in beets better than starch to not feed unhealthy bacteria? The GAPS diet advocates the elimination of starch because they feed the bad bacteria--but would a non-ketogenic diet that has a lot of squash and beets and the "sugary" vegetables feed it just as much?

Depression and serotonin deficiency often accompanies a low body weight and malnutrition. I have heard concerns of low serotonin and cortisol levels on a low-carb diet (but it is not defined what "low" is). How grams of carbs, or ratio of calorie consumption, does one need to CREATE good serotonin and cortisol levels?

Thank you so much!