Let's get a few facts straight about food. Facts that are supported by real hard data, not someone's idea of how things should be done.
First, food quality in the Western World is exceptional. Food poisonings are extremely rare and very few illnesses are caused by tainted foods or water. Availability of good food and clean water have been major contributors to better average longevity. These contributions far exceed the contributions made by the medical profession, except for vaccines. It is probably fair to say that we live long lives primarily because of clean water, good quality food, and proper sewage systems.
Second, diets in the West are another matter altogether. Most Western diets are not healthy as evidenced by the obesity epidemic. The diets are too high in calories, too salty, and too high in carbohydrates. Food consumption in the West is no longer driven by hunger or need, but by desire. Too much food is available and too much time is spent eating and drinking, leading to excess intake. Most food items have also been manipulated to an artificial but highly desirable sweetness, saltiness, and spice level that is meant to promote overeating and is making food an addictive substance. Seasonal intake patterns have been removed leading to further excesses.
Thirdly, people are largely independent of their diet. Adults can survive and thrive on anything from an almost purely carnivorous to an almost purely vegan diet. And if properly conditioned, they can do effective work on pretty much any diet too. The contributions of diet to performance are minimal within a large parameter range. As long as there are no significant chronic deficits (and these are extremely hard to come by in the West), performance will not be impaired. Children are more sensitive, but even children rarely develop deficits in the US or Western Europe.
Fourth, there is no need for supplements, minerals, or vitamins apart from those present in natural foods. There is no evidence that such concoctions have any benefit whatsoever, and in many cases, serious adverse effects have been demonstrated. There are more problems with vitamin overdose than with lack of vitamins in the West. No supplement has ever been shown to be beneficial in a prospective study and many have been shown to promote the very illnesses they were supposed to cure. Despite being a multi-billion dollar industry that grows at double digit rates, the supplement industry serves no purpose other than consumerism. There is no scientific evidence that a "multi-vitamin" is good for you, but there is some evidence that it can harm you.
Despite all the hoopla and recommendations, performance in endurance events is not affected by diet and endurance events do not require a "special diet." There are two important exceptions to this rule.
The first relates to having an upset stomach. Ignoring infectious causes, the most common culprit is slow digestion and uptake. That can happen when the workload is too high for too long or when the person is not well adjusted to the diet or both. You will not do well eating French fries while cycling unless you are used to doing so and unless you can reserve some of your cardiac output to digestion (i.e. you are not at your maximal heart rate for an extended period of time). In general, since fats take longer to digest, eating a lot of fat while exercising is not recommended but some people can do well eating fats and competitors have done well in RAAM eating cheeseburgers, pizza, and fries.
There are no performance or health advantages to a liquid diet. If the liquid diet is well balanced, there are no disadvantages either. It is a matter of personal preference.
Heavy workloads call for no food or easily digested items. Carbohydrates are the easiest to digest and result in the fastest energy delivery. Only anaerobic episodes or prolonged exercise require additional intake. You can easily run a marathon without eating or drinking and do very well too.
The type of activity also matters. Running is easily the most sensitive to eating and to eat while running requires training. Apart from high workloads and sweating that can lead to electrolyte imbalances (the gut is sensitive to electrolyte levels), running also causes bouncing and seems to promote diarrhea in sensitive individuals. Many elite distance runners experience an occasional embarrassing event.
Running is almost entirely done on fatty acids derived from stored fats. There is no need to eat while running unless you run for more than a day on end.
The second problem is weight. Weight is the number one enemy of the endurance athlete. It matters less in some sports, such as swimming or track riding, but it is totally detrimental to other sports such as running.
There is overwhelming evidence to support the notion that carbohydrate-rich diets promote weight gain. Diets rich in fats (the French diet is very fat-laden) often lead to the lowest steady weight and are best to induce weight loss. This is contrary to the prevailing view of the medical establishment and nearly every nutrition science publication. Yet it has been repeatedly demonstrated in large studies.
The prevailing "medical" view however, is not based on science, but appears rooted in prejudice, as many investigational journalists have clearly illustrated.
Diets high in fats, even saturated fats, do not cause weight gain. They also do not cause or contribute to heart disease, diabetes, or metabolic syndrome. If anything, carbohydrate rich diets are the more likely culprit. However, before pointing the finger at any diet, it is good to remember that genetics plays a much bigger role than diet does. And the worst part of a diet is the quantity of calories consumed, not the composition of the diet per se.
Bon Appetit to all.