koped this from my online course:

When people get up in the morning their blood sugar levels are usually good, but they decline rapidly with the morning's activity. Most people don't feel like eating and many try to get by with a cup of coffee or some cereal and toast. This sort of meal, even if supplemented with orange juice and bacon, is high in carbohydrate and causes sugar levels to peak rapidly but about an hour later they drop dramatically.

The effect is even worse if a person eats food high in sugar such as jam, doughnuts or sweet pancakes. This peak followed by the drop in blood sugar causes feelings of fatigue and irritability and makes concentration difficult. People who eat protein in their breakfast, such as eggs or fortified milk (milk with skim milk powder or protein powder added) elevate their blood sugar to a good level and it stays consistently high throughout the morning.

Studies have shown that no matter what a person eats after having no breakfast or a high carbohydrate breakfast, they are susceptible to fatigue and irritability for the rest of the day. It is now generally accepted that people should eat breakfast (with protein) to be able to function for a full day (Davis, 1976; Eades & Eades, 2000; Holford, 2005; Wills, 2000).

Many people drink coffee or tea as a starter for the day. The caffeine in these drinks artificially allows the body's levels of adrenaline and dopamine to rise. Adrenaline is a ‘heart starter' and dopamine promotes a sense of well being and alertness. However, because caffeine has artificially stimulated this result, the body's natural regulation is interfered with and caffeine is needed to continually keep the body stimulated.

In other words, coffee and tea drinkers become addicted to caffeine. Over time, this may lead to a higher tendency towards apathy, depression and exhaustion. After only a few weeks of using caffeine, people must either continually boost the levels to get the same result. However, people usually start to lapse into the phase of fatigue and poor concentration. The solution is to stop drinking these sorts of drinks and to allow three or four weeks for the body to readjust. The feelings of fatigue and heaviness will pass (Holford, 2005).