Food is fuel -- plain and simple. Through digestion, your body uses nutrients in food to give you energy, make repairs, create new cells and run all kinds of metabolic processes. Without proper nourishment, though, your body starts running on empty. Extreme fatigue is one of the key signs that you’re not eating enough. Think about it: Your car won’t go very far once it runs out of fuel. The same is true for your body.
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Your body runs on glucose, the simplest form of carbohydrate. Glucose fuels all cells. When glucose runs low after you haven't eaten for a while, cells can’t function and you’ll feel rundown. You’ll probably be unable to concentrate, too. Brain cells use twice as much energy as other cells, The Franklin Institute reports. When glucose isn’t around, your brain has a harder time staying sharp. This cause of fatigue and poor focus can be reversed quickly, simply be eating something with carbohydrates.
Minimal Energy Production
Your body relies on a multitude of B vitamins to produce energy. Riboflavin, thiamine, folate, B-12, pantothenic acid, B-6, niacin and biotin work as a team to power your metabolism. They’re the nutrients responsible for extracting energy from fat, protein and carbohydrates -- in the form of calories -- so you have fuel to function. When you’re not eating enough, though, you’re probably not getting enough of the B vitamins, resulting in a lack of energy. The B vitamins are water-soluble and don’t stay in your system for an extended period. Eat something that’s full of various B vitamins, like meat, poultry, dairy, whole grains, eggs, nuts or legumes. These nutrient-dense foods should supply some of the B vitamins you’re missing, so you can feel energized again.
Poor Oxygen Transportation
One of the reasons you’re always tired when you don’t eat enough is because you’re likely not getting enough iron. Having an inadequate iron intake leads to iron-deficiency anemia over time. Your body can't keep up with the high demand of making new red blood cells. Or when you do produce red blood cells, they are abnormally small. This minimizes oxygen transportation to cells. You’re left feeling weak, tired, grumpy and probably unable to concentrate well. Building your iron levels back up takes time. Your health care provider can set you up on a treatment plan, although your fatigue won’t go away overnight.
Electrolytes, including potassium, sodium and calcium, are the minerals in foods that help with electrical impulses. Each cell in your body stores electrolytes, allowing energy to transfer from cell to cell. The problem with not eating enough is that your electrolytes could run low over time. Feeling weak, fatigued and having muscle spasms are all side effects of low electrolytes. If you routinely don’t eat enough, it’ll take some time for your electrolytes to become imbalanced, but it can seriously affect your health, including your heart functions.