Charaka devoted an entire chapter of the Charaka Samhita to nidra(sleep). He ranked it as one of the three pillars of health, equal in importance to food and brahmacharya (disciplined living). His argument: you can eat perfectly and practice consistently, but if the quality of your sleep is compromised, neither of the other two can fully deliver. Sleep is where digestion completes, where tissue repairs, where the nervous system clears its load. Nothing substitutes for it.

He then spent considerable space describing what destroys it.

The first culprit was Agni, asking the digestive system to do heavy work during the hours when its capacity is lowest. Agni, in Charaka's model, follows the arc of the sun. It peaks at noon and drops significantly after sunset. A heavy meal late in the evening, and sweet, dense food is the heaviest category in Ayurvedic classification asks a low-capacity system to do high-capacity work. The body responds by running metabolic processes that elevate core temperature, delay the natural nighttime drop in body heat, and keep the nervous system in a more activated state than sleep requires. You lie down. You feel awake. The barfi after dinner isn't the problem. The barfi at 11pm is.

The second culprit was kapha excess in the evening hours. Sweet food specifically increases kapha, which is the heavy, cool, stable quality. In the right proportion, kapha promotes sleep. In excess, it creates a heaviness that disrupts the early sleep cycles, particularly the deeper slow-wave stages that do most of the restorative work. The sugar spike is one mechanism. The sheer caloric density landing on a low-Agni system is another.

The third culprit was irregular timing. Charaka specified that the body has a natural sleep window, roughly in line with what chronobiology now calls the circadian sleep phase. The body begins cooling, releasing melatonin, and shifting toward parasympathetic dominance in the early evening. If you are still eating, bright-lit, stimulated, and socially active during this window, you are working against a biological tide. You can do it, but you will pay in sleep quality and you will feel the debt the next day.

Here's the modern translation.

The research on late-night sugar consumption and sleep is consistent: eating high-glycemic food in the two hours before sleep increases nighttime wakefulness, reduces slow-wave sleep, and elevates morning cortisol compared to an earlier finish or a lower-glycemic evening meal. The mechanism is the blood sugar response followed by the counter-regulatory drop, which is a mild physiological stressor that activates the sympathetic nervous system at precisely the moment the body is trying to wind down.

The solution Charaka prescribed was not abstinence. It was timing. Finish eating at least two hours before sleep. If something sweet is part of the meal, have it during the meal. Keep the post-dinner period to herbal tea, warm milk, light conversation. Nothing that requires significant metabolic work.