Final answer:
The exact increase of body fat from a 30 day McDonald's diet isn't specified, but excess calorie consumption can lead to increased body fat. High fat and sugar content in fast food contribute to risks of obesity and related health problems. The actual fat gain would depend on caloric excess and individual metabolism.
Step-by-step explanation:
The increase of body fat as a result of eating nothing but fast food, such as from McDonald's, during a 30 day experiment is not explicitly stated in the given information. However, we can infer that consuming excess calories, particularly from high-fat foods, can lead to excessive body fat accumulation. It's known from the data provided that if an individual consistently consumes more energy than expended, this leads to fat storage, with an extra 3,500 Calories resulting in almost half a kilogram (1 pound) of stored body fat. Therefore, if the fast-food diet significantly exceeded the individual's caloric needs, there could be a considerable increase in body fat percentage over 30 days. The detrimental effects of fast food are often associated with high fat and sugar content, leading to an increased risk of obesity, type 2 diabetes, and hypertension, along with other health issues.
Moreover, foods high in sugar and low in fat still contribute to obesity, as the body converts excess sugar into fat. This is partly because some low-fat or non-fat foods compensate for texture and flavor by adding sugar, which then contributes to the same caloric excess that leads to weight gain and an increase in body fat. Given this information, any increase in body fat would depend on the specific excess of calories consumed as well as individual metabolic factors.