Krishna lays down a principle of balance. Four kinds of people will struggle with yoga: the one who eats too much, the one who fasts too severely, the one who sleeps all day, and the one who refuses sleep altogether. Both extremes — overindulgence and extreme austerity — block the path.
This is remarkably practical advice. A body stuffed with food grows sluggish, and the mind follows into dullness. A body starved of nourishment grows weak, and the mind cannot hold steady. Too much sleep breeds laziness; too little sleep breeds agitation. Neither state supports concentration.
Krishna is not prescribing a rigid diet or sleep schedule. He is pointing to a middle way — where the body has enough fuel and enough rest to function well, without tipping into excess on either side. The pivot point of yoga is balance, not deprivation.