http://www.leangains.com/2010/10/top-ten-fasting-myths-debunked.html zei:
7. Myth: Skipping breakfast is bad and will make you fat.
Truth
Breakfast skipping is associated with higher body weights in the population. The explanation is similar to that of lower meal frequencies and higher body weights. Breakfast skippers have dysregulated eating habits and show a higher disregard for health. People who skip breakfast are also more likely to be dieting, thus by default they are also likely to be heavier than non-dieters. Keep in mind that most people who resort to breakfast skipping are not the type that sit around and read about nutrition. They are like most people dieting in a haphazard manner. The type to go on a 800 calorie-crash diet and then rebound, gaining all the weight (and then some) back.
Sometimes, an argument is made for eating breakfast as we are more insulin sensitive in the morning. This is true; you are always more insulin sensitive after an overnight fast. Or rather, you are always the most insulin sensitive during the first meal of the day. Insulin sensitivity is increased after glycogen depletion. If you haven't eaten in 8-10 hours, liver glycogen is modestly depleted. This is what increases insulin sensitivity - not some magical time period during the morning hours. Same thing with weight training. Insulin sensitivity is increased as long as muscle glycogen stores aren't full. It doesn't disappear if you omit carbs after your workout.
Origin
First of all, we have the large scale epidemiological studies showing an association with breakfast skipping and higher body weights in the population. One researcher from that study, commenting on the association with breakfast skipping or food choices for breakfast, said:
"These groups appear to represent people 'on the run,' eating only candy or soda, or grabbing a glass of milk or a piece of cheese. Their higher BMI would appear to
support the notion that 'dysregulated' eating patterns are associated with obesity, instead of or in addition to total energy intake per se."
Kellogg's and clueless RDs love to cite them over and over again, so people are lead to believe that breakfast has unique metabolic and health-related benefits. In reality, these studies just show breakfast eaters maintain better dietary habits overall.
Other studies frequently cited claiming that breakfast is beneficial for insulin sensitivity are all marred with methodological flaws and largely uncontrolled in design.
In one widely cited study, subjects were entrusted to eat most meals in free-living conditions. The breakfast skipping group ate more and gained weight, which affected health parameters negatively.
From the abstract: "Reported energy intake was significantly lower in the EB period (P=0.001), and resting energy expenditure did not differ significantly between the 2 periods." EB = eating breakfast. In essence, people who ate breakfast could control their energy intake better for the rest of the day. They didn't gain any weight but the breakfast skipping group did. Fat gain always affects insulin sensitivity and other health parameters negatively. Thus what people took this to mean is that breakfast is healthy and improves insulin sensitivity. Which isn't at all what the study showed.