When blood glucose gets low, your energy plummets and you may find it hard to concentrate. Your body can temporarily fill the gap by drawing on glucose stored in your liver, but those supplies are limited. When they run out, your body can produce glucose from fats and proteins. Fats are good for backup energy, but your body doesn't like to divert protein into energy due to its other vital functions. The best way to keep your body fueled is to consume the right amount of fats, proteins and carbs.
Carbohydrates consist of molecules of sugar, which your body digests into glucose and uses for energy. When you're short on carbs, glucose can be created from fat and protein in a process called gluconeogenesis. Gluconeogenesis takes place mostly in your liver, which also has the job of maintaining a steady amount of glucose in your blood. If blood sugar drops too low due to problems in the liver, your kidneys can boost blood sugar by converting the amino acid glutamine into glucose.
The saturated and unsaturated fats in your diet consist of two substances bound together: glycerol and fatty acids. During digestion, they're separated, and each one follows a different path. Glycerol is easily metabolized and used to make glucose. Fatty acids are carried to tissues throughout your body, where they help build cell walls, produce hormones and digest fat-soluble nutrients. Fatty acids can be converted into another substance called acetyl CoA, which is used to create energy, but they're not turned into glucose.
Turning Protein into Glucose
After you eat protein-containing foods, they're digested and broken down into individual amino acids, which cells then use to rebuild new proteins. Amino acids also have a variety of other jobs, such as helping to produce neurotransmitters and antioxidants. Your body can use all of the amino acids except lysine and leucine to make glucose. Some of the amino acids have the ability to become glucose and fatty acids, while lysine and leucine can only be used to synthesize fatty acids.
The recommended intake for carbohydrate is based on its role as the most important source of energy. Getting enough carbs also ensures that protein is not turned into glucose. When protein is used for energy, it's not available to build muscles, synthesize antibodies, support metabolism or perform any of its life-sustaining roles. The Institute of Medicine recommends that 45 percent to 65 percent of your daily calories should be carbs. Fats should account for 20 percent to 35 percent of your calories, while proteins should fill the remaining 10 percent to 35 percent. Enjoy poultry, fish, lean meat and beans for protein. Meet your fat intake with unsaturated fats from vegetable oils, nuts and seeds. Support long-term energy with complex carbs, such as brown rice, oatmeal, quinoa, whole-grain breads, peas, beans and lentils.
- Medical Biochemistry Page: Gluconeogenesis - Endogenous Glucose Synthesis
- Elmhurst College: Lipid Catabolism Summary
- College of the Canyons: Fat
- Medical Biochemistry Page: Introduction to Amino Acid Metabolism
- Biochemistry: Amino Acids Are Precursors of Many Biomolecules
- Institute of Medicine: Dietary Reference Intakes - Macronutrients