When you eat food like breads and cereals or sugar based foods and drinks, they release sugars into your body. These sugars are broken down quite quickly (within a few hours) and then you run out. When you run out of sugars in your blood, you feel dizzy and light headed due to low blood sugar levels.
If you have meat and vegetables instead of breads and cereals, the meat and veg take longer to release nutrients and they don't release sugars. The meat and veg gives you a more steady supply of nutrients and energy that are a bit harder to digest than sugars, but they don't screw up your pancreas like sugars do.
If you consume a lot of foods with flour or sugar in, you are more likely to have massive fluctuations in blood sugar levels, including low blood sugar, and more likely to develop heart disease and Type 2 Diabetes.