The discussion highlights that while diet does affect longevity, the most significant factor is maintaining a healthy body weight rather than focusing on specific dietary choices like vegan or carnivore. The speaker suggests that being excessively overweight can reduce lifespan significantly, whereas the difference in longevity between different diets is relatively minor if body composition is similar. The emphasis is on consuming mostly healthy, unprocessed foods to aid in weight control, which is crucial for longevity. However, the speaker also notes that stressing over perfect dietary habits can be counterproductive, as the stress itself may negatively impact lifespan. Instead, a balanced approach that includes occasional indulgences without guilt is recommended. The conversation also touches on the psychological aspects of diet, suggesting that an overly neurotic approach to eating can be more harmful than occasional dietary imperfections.