Fatigue is one of the main symptoms of not eating enough. You get energy from the foods you eat in the form of calories. When your calorie intake is too low, your body can't carry out physiological functions and support daily activity. In addition, not eating enough of certain types of foods can leave you low on energy.
Not eating enough often causes fatigue.
How Your Body Gets Energy
Calories are units of energy. All foods contribute calories to your diet, some more than others. One calorie, as expressed on the nutrition information on a food package, is actually a kilocalorie, or 1,000 calories. It's the amount of energy needed to increase the temperature of 1 kilogram of water by 1 degree Celsius.
Calories help your body function by providing energy in the form of heat. To fuel physiological functions like respiration and digestion, along with daily activities of living and exercise, your body burns the calories it gets from digesting the foods you eat. When your calorie intake is low, your body is essentially like a gas tank running on empty. Eventually, your car will stall and cease functioning.
How Many Calories You Need
Your daily calorie needs depend on several factors, including your age, gender and activity level. Men typically need more calories than women, older people need fewer calories than their younger counterparts and active people need more calories than those who are sedentary.
Determining how many calories you need to function and thrive isn't an exact science. You can consult your doctor or a nutritionist to get a more exact number, but in the meantime, you can use the Dietary Guidelines for Americans for a rough estimate.
According to the guidelines, moderately active women ages 26 to 50 need 2,000 calories a day. Women in that same age group who are active need 2,200 to 2,400 and those who are sedentary need 1,800 to 2,000.
Moderately active men ages 21 to 50 need 2,400 to 2,800 calories each day, while active men in that age group need 2,800 to 3,000 calories daily. Sedentary men ages 21 to 50 need 2,200 to 2,400 calories.
Reducing Calories for Weight Loss
To lose weight, you need to eat fewer calories than your body needs each day. This causes your body to burn stored energy, or fat. But a common dieting mistake people make is cutting too many calories. This can lead to fatigue and actually stall weight-loss goals.
Generally, women should not eat fewer than 1,200 calories per day, and men shouldn't eat less than 1,500 calories. Going below this increases the risk of fatigue as well as nutrient deficiencies. In addition, when you're tired from not eating enough, it's hard to increase your activity level, which is a key part of the weight-loss equation.
The only time you should eat less than the recommended minimum is if you're following a medically administered very low calorie diet, or VLCD. Doctors prescribe these short-term extreme diets for people who are obese and whose weight poses immediate problems for their health. In this case, the diet is carefully balanced and monitored by a medical professional to avoid serious consequences.
Energy From Carbohydrates
The low-carb dieting craze has many people thinking carbs are the enemy. But you need adequate carbohydrates to function, because they're your body's primary source of energy. Carbs are broken down into glucose and used as an immediate source of energy for your body and brain. Your brain uses almost half of that energy, and brain functions such as thinking, learning and memory are dependent upon an adequate supply.
It's true that any carbs that aren't used immediately for energy turn to fat in the body — but any macronutrient not used to fill an immediate need is stored as fat. It's also true that a high intake of carbohydrates may lead to metabolic disorders and Type 2 diabetes; however, this doesn't apply to all carbs, only to simple carbs.
Complex vs. Simple Carbs
Simple carbohydrates are simple in chemical structure. Your body digests them easily and releases them to the bloodstream quickly. When insulin, the hormone that helps usher sugar into cells, can't keep up with the tide of sugars, they're left to float freely in the blood, leading to high blood sugar. Over time, high blood sugar is harmful to health. Simple carbs are those from foods and beverages like cake, candy, soda, fruit juice, white rice, white bread and white pasta.
Complex carbs, found in fruits, vegetables and whole grains, do not pose this risk. They're more complex in structure, and your body digests them more slowly, leading to a steady supply of glucose to your cells. This slow digestion is due, in part, to dietary fiber, the part of plants that your body can't digest. Fiber not only slows absorption of blood sugar, but increases satiety after a meal.
How Many Carbs You Need
Many low-carb diets call for getting less than 20 percent of your daily calories from carbs. This limits your intake of a lot of healthy foods and commonly leads to fatigue and other problematic symptoms. According to the National Academy of Medicine, adults should get between 45 and 65 percent of their daily calories from carbs. On a 2,000-calorie diet, that's 225 to 325 grams of carbs per day, since carbs have 4 calories per gram.
If you're going to cut carbs, cut out simple carbs. Keep tabs on your energy level. If you feel fatigued, you may need to increase your carb intake, if not your total calories.
Energy From Protein and Fats
Protein and fats also contribute calories. Protein has 4 calories per gram and fat has 9 per gram. People trying to reduce their calorie intake may reduce their fat intake because fat is more calorific than protein or carbs. But getting enough of both protein and fats is essential for maintaining your energy level and staying healthy. When you're not getting enough calories, it can be challenging to get the amounts of protein and fat you need each day.
Fats supply your body with energy when carbohydrates aren't present. After about 20 minutes of exercise, your body starts using fat for energy. If there isn't enough fat, your body taps into your protein stores, breaking down skeletal muscle for energy. Losing lean muscle mass will ultimately make it harder for you to lose weight, because lean muscle increases resting metabolism.
Fatigue is often the first warning sign your calorie intake is too low. But there are other harmful symptoms that can clue you in to the problem:
- Hair loss
- Sleep disturbances
- Feeling cold all the time
- Constant hunger
If you worry that you aren't eating enough, track your diet and calorie intake for a few days and see how it compares to your daily needs. You might be surprised to find out how little you're actually eating, even if it seems like you're eating a lot.
Although there's a focus on overeating in the health and nutrition world, undereating is also a common and serious problem that can have just as many ill effects on your health. Your doctor or a nutritionist can help you formulate a plan to increase your calorie intake so you feel energetic and healthy every day.
- Scientific American: How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods?
- Dietary Guidelines for Americans: Appendix 2. Estimated Calorie Needs per Day, by Age, Sex, and Physical Activity Level
- BeachBody on Demand: What’s the Minimum Calorie Intake You Should Consume When Dieting?
- WebMD: Very Low-Calorie Diets: What You Need to Know
- Harvard Medical School: Sugar and the Brain
- BMJ: Carbohydrate Intake, Obesity, Metabolic Syndrome and Cancer Risk? A Two-Part Systematic Review and Meta-Analysis Protocol to Estimate Attributability
- Mayo Clinic: Are You Getting Too Much Protein?
- Diabetes.co.uk: Simple vs. Complex Carbs
- Dr. Kellyann: Put the Break on Your Fat Storing Hormones
- Nutrition Reviews: Dietary Fiber and Satiety: The Effects of Oats on Satiety
- Diet Doctor: How Low Carb Is Keto?
- National Academy of Medicine: Dietary Reference Intakes: Macronutrients
- Applied Physiology, Nutrition and Metabolism: Effects of Short-Term Energy Deficit on Muscle Protein Breakdown and Intramuscular Proteolysis in Normal-Weight Young Adults
- MedlinePlus: Dietary Fats Explained
- Healthline: 9 Signs That You're Not Eating Enough
- Chris Kresser: Are You An Under-Eater? 8 Signs You’re Not Eating Enough