Short answer: Ayurveda's answer is agni - digestive strength. The texts say food only nourishes the body when agni processes it well; what is not processed becomes ama, a residue that builds nothing. The classical fix is to strengthen digestion first, then nourish with bruhana (building) foods like milk, ghee, dates, ashwagandha and shatavari, taken daily in moderate amounts, or as directed by the physician.
"I eat everything, nothing sticks." If you have said this, you already know the usual advice - eat more, drink a gainer - does not work for you. Ayurveda would say the advice skips the real problem.
The gut comes first
In Ayurveda, food becomes body tissue only if agni processes it properly. The texts list what weakens it: irregular meal times, heavy cold and packaged food, stress and poor sleep. The Charaka Samhita's nourishing (bruhana) guidance starts with digestion for exactly this reason.
A practical classical routine
- Eat at fixed times, warm and freshly cooked where possible, for 2-3 weeks before judging anything.
- Add nourishing foods daily: milk (plain or as a malt preparation), a spoon of ghee in meals, soaked dates and nuts.
- Consider classical nourishing herbs - ashwagandha and shatavari are the two most cited in the texts, and ashwagandha has been tested in Indian randomised trials for strength and recovery - as directed by the physician.
- Lift light weights or do bodyweight exercise 3 times a week, so new nourishment becomes muscle rather than fat.
- Keep a steady sleep schedule. The texts treat regular sleep as a pillar of building strength.
When to see a doctor
If you are losing weight without trying, or weight won't rise despite months of effort, get checked for thyroid, gut and blood-sugar issues first. Ayurveda works alongside a diagnosis, not instead of one.
More on this topic: our Weight Gain guide.
Sources: Charak Samhita Online Edition (bruhana chapter), carakasamhitaonline.com; "Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial", PMC4658772, pmc.ncbi.nlm.nih.gov/articles/PMC4658772/; "Plant profile, phytochemistry and pharmacology of Asparagus racemosus (Shatavari): A review", PMC4027291, pmc.ncbi.nlm.nih.gov/articles/PMC4027291/. Reviewed by Dr. Renjith N. Raj, BAMS (Reg. No. 17120).