The Prophet Muhammad ﷺ said: "The son of Adam does not fill a vessel worse than his stomach. It is sufficient for the son of Adam a few morsels to keep his back straight. If he must do more, then: one third for his food, one third for his drink, and one third for his breath." (Narrated by At-Tirmidhi, no. 2380, and Ibn Majah, no. 3349, from Al-Miqdam ibn Ma'dikarib).
This hadith, narrated by Al-Miqdam ibn Ma'dikarib, recommends moderate eating: to fill the stomach only one third with food, one third with drink, and leave one third empty. Modern nutritional science has confirmed the profound benefits of this moderation.
Research on caloric restriction (reducing energy intake by 20-30% without malnutrition) has shown in many model organisms — yeast, worms, flies, mice — a significant increase in lifespan and a slowing of aging. Studies published in the journal Nature have shown that aligning food intake with circadian rhythms (eating early, fasting at night) improves metabolism and reduces the risk of metabolic diseases.
The US National Institute on Aging (NIA) conducts extensive research on the mechanisms of caloric restriction, notably the activation of autophagy — a cellular "cleaning" process that removes damaged components and protects against age-related diseases.
The prophetic principle of the "third" — not filling the stomach — thus aligns with modern recommendations for dietary moderation and discoveries on the benefits of caloric restriction for health and longevity. The convergence is solid.