On one hand, some believe that intermittent fasting, which essentially extends the overnight fast, decreases blood sugar and insulin levels, and triggers hormonal changes in your body to accelerate fat loss. On the other hand, some believe that eating breakfast helps to kick-start your body's metabolism and thereby increase fat loss. So, why am I stating that the "skipping breakfast is bad" theory is a myth?
Many people, when defending that skipping breakfast is detrimental to your health, refer to studies that show that breakfast eaters are less likely to be overweight and have a lower risk of chronic diseases. While all these studies are true, these are merely observational studies that don't demonstrate causation (1). In other words, these studies do not prove that breakfast was the determining factor causing the results. It may be that regular breakfast-consumers tend to be of higher socioeconomic status (as they can afford breakfast), work on daytime schedules (no night shifts), and generally have more consistent habits than breakfast-skippers (e.g. breakfast-consumers generally smoke and drink less, and exercise more) (2). Randomized controlled trials actually suggest that whether you eat or skip breakfast actually has no observable impacts on your health or weight.
Some people also claim that eating breakfast kick-starts your metabolism due to the thermic effect of food. But actually, what affects the metabolism is the type of food eaten and the total amount of food consumed throughout the day, no matter the time and frequency of meals. The Asian Oceanian Association for the Study of Obesity conducted a randomized controlled trial and concluded that there is no difference in calories burned over a 24-hour period between breakfast consumers and skippers (3).
On the other hand, skipping breakfast might help towards reducing overall calorie intaking (as you are cutting out an entire meal from your day), and intermittent fasting, which requires skipping breakfast, has also been shown to have numerous benefits for weight loss and overall health.
So, the myth that skipping breakfast is unhealthy is false. If you enjoy breakfast, sure, go for it. But if you don't feel like eating breakfast, know that it won't be detrimental for your health.