He spent a lot of time living only off the alms that other people were generous enough to donate, as dictated by his ascetic lifestyle. At the time, anyone who followed this path of extreme austerity was expected to eat whatever was placed in their begging bowls. This sometimes meant eating things that were unhealthy, perhaps even rotten, or would require them to break their vows of veganism. It was symbolic of their gratitude for the kindness of strangers.
While some modern monks still follow this tradition and take vows of poverty, it is not common in lay Buddhist practice.
Siddhartha Gautama ceased his fasting when his hunger became too much for him to bear. While living exclusively off the nourishment of one nut or leaf per day, he collapsed and nearly died. He was lucky enough to be revived by a passing girl.
The energy granted him by a proper meal gave him time to reflect on the decisions he had made. After that, he did not deprive himself so much, but rather attempted to live in moderation. He ate enough to ensure that he did not starve, but did not indulge in excess amounts of food.
This is the foundation of the typical Buddhist diet.
In modern monasteries, food is shared. Everyone contributes to making meals and eats together. They eat enough to give them the energy them need for any daily tasks they have. Traditionally, an early morning meal is eaten at the beginning of the day and another in the middle of the day. In some monasteries, an evening meal is also made, but not all. Some see an additional meal at the end of the day as unnecessary, as there is no need for any more energy immediately before bed. The institutions that do provide an evening meal do so fairly early on.
No monasteries provide snacks, though some have fruit bowls, and none allow monks to have their own private stores of food to eat outside of communal mealtimes. This ensures that no one over indulges and that everyone gets the nutrition they require.
Generally, monks follow a strict vegetarian, and sometimes vegan, diet as part of their vow to never be the cause of harm to other living creatures. Synthetic sweet or sugary foods are rare, often absent entirely.
While this is not enforced on lay Buddhists, it sets an example for them to follow and its basic guidelines can be applied to anyone living a modern life.
Eat as much food as you need to provide the energy you need to get through your day. Anything else is an indulgence. While the schedule followed by strict monks won’t be particularly practical for someone working a full time job, its fundamental purpose is still fairly easy to achieve.
Making your own meal, or sharing the workload with friends or family, will bring a deeper sense of satisfaction to it all. Avoiding snacks, or limiting snacks to only fruit, will ensure that you don’t over indulge and that your overall intake is healthy.
As with most of the guidelines set by the Buddhist tradition, there are no strict rules to dictate what a person does or does not consume outside of the monastery setting. But the behaviour of the most devout act as a reliable guide for anyone attempting to bring Buddhism into today’s world.