your calorie needs
However, you're more likely to think of calories as a measure of the energy your body gets from the foods and drinks you eat.
Your body needs calories to function and uses them to maintain three major processes:
- Basal Metabolic Rate (BMR): This refers to the number of calories you need for basic functions, including the normal functioning of your brain, kidneys, heart, lungs, and nervous system.
- Digestion: Your body uses a certain number of calories to digest and metabolize the food you eat. This is also known as the thermic effect of food (TEF).
- Physical activity: This refers to the number of calories needed to provide you with energy for daily tasks and exercise.
Generally speaking, eating more calories than your body needs results in weight gain, primarily in the form of body fat. Eating fewer calories than your body needs can lead to weight loss.
This concept of calorie balance, which is backed by strong scientific research, is why people who want to lose weight often try to limit their calorie intake.
However, restricting calories too much can harm your health in these 5 ways.
1. It can slow down your metabolism
Multiple studies have shown that a low-calorie diet can reduce the number of calories your body burns by up to 23%.
What's more, this lower metabolism can persist long after the calorie-restricted diet is discontinued.
In fact, researchers believe this lower metabolism may partially explain why more than 80 percent of people regain weight after stopping a calorie-restricted diet.
One of the ways that a calorie-restricted diet slows metabolism is by causing muscle loss.
This loss of muscle mass is especially likely to occur if a calorie-restricted diet is low in protein and not combined with exercise. To prevent your weight loss diet from affecting your metabolism, make sure you never eat fewer calories than you need to maintain your BMR.
It may also be helpful to increase your protein intake slightly and add resistance exercises to your exercise routine.
2. It can cause fatigue and nutritional deficiencies
For example, a calorie-restricted diet may not provide adequate amounts of iron, folate, or vitamin B12. This can lead to anemia and extreme fatigue.
Additionally, the amount of carbohydrates you eat may contribute to fatigue.
Some research suggests that calorie-restricted, low-carb diets may cause fatigue in some people.
However, other studies have found that low-carb diets can reduce fatigue. Therefore, this effect may depend on the individual.
A calorie-restricted diet may also limit other nutrients, including:
- Protein: Not eating enough protein-rich foods such as meat, fish, dairy, beans, peas, lentils, nuts and seeds can lead to muscle loss, thinning hair and brittle nails.
- Calcium: Not eating enough calcium-rich foods such as dairy products, green leafy vegetables, calcium-cured tofu and fortified milk may reduce bone strength and increase the risk of fractures.
- Biotin and Thiamine: Low intake of whole grains, legumes, eggs, dairy, nuts, and seeds may limit the intake of these two B vitamins, which may lead to muscle weakness, hair loss, and scaly skin .
- Vitamin A: Not eating enough foods rich in vitamin A, such as organ meats, fish, dairy products, green leafy or orange fruits and vegetables, may weaken your immune system and cause permanent eye damage.
- Magnesium: Insufficient intake of magnesium-rich whole grains, nuts, and leafy green vegetables may lead to fatigue, migraines, muscle spasms, and cardiac arrhythmias.
To prevent fatigue and nutritional deficiencies, avoid excessive calorie restriction and make sure to eat a variety of whole, minimally processed foods.
3. It may reduce fertility
More specifically, increased levels of estrogen and luteinizing hormone (LH) are required for ovulation to occur.
Interestingly, research shows that LH levels depend in part on the number of calories in a woman's diet.
As a result, studies have shown that women who consume 22-42% fewer calories than they need to maintain their weight have suppressed reproductive function.
Insufficient caloric intake may also lower estrogen levels, which is thought to have lasting negative effects on bone and heart health.
Signs of declining fertility may include irregular or absent menstrual cycles. However, mild menstrual irregularities may not have any symptoms, so a more thorough medical test may be needed to confirm the diagnosis.
Researchers believe that severe caloric restriction may also affect male reproductive function, but there is little research on the topic.
4. It weakens your bones
That's because calorie restriction can lower estrogen and testosterone levels. Low levels of these two reproductive hormones are thought to reduce bone formation and increase bone breakdown, leading to weaker bones.
Additionally, calorie restriction—especially when combined with physical exercise—can increase stress hormone levels. This can also lead to bone loss.
Bone loss is particularly troublesome because it is often irreversible and increases the risk of fractures.
5. It may lower your immunity
This applies to viruses like the common cold, and is especially true when it's combined with high levels of physical activity.
For example, one study compared athletes who focused on slimming down (such as boxing, gymnastics, or diving) with athletes who were less focused on weight.
Researchers report that athletes who need to lose weight try to lose weight more frequently and are nearly twice as likely to have gotten sick in the past three months.
In another study, kickboxing athletes who dieted to lose weight a week before a competition had decreased immunity and increased risk of infection.
The effects of caloric restriction in inactive individuals are unclear, and more research is needed before strong conclusions can be drawn.
How to eat the right number of calories
Determining the number of calories that works for you will reduce your likelihood of experiencing the negative health consequences mentioned above.
There are several ways to estimate your own calorie needs. The simplest method involves three simple steps:
- Determine your BMR: Use this online calculator to estimate the minimum number of calories your body needs each day. The goal is to never consume fewer calories than this.
- Estimate your daily needs: Use this online calculator to estimate the number of calories you need to maintain your current weight.
- Determine your weight loss calorie needs: If weight loss is your goal, your daily calorie intake should fall between the amount needed to maintain your BMR and the amount needed to maintain your current weight.
Also, be sure to record your meals in an online food diary, such as the Crono Chart, at least at the beginning of your weight loss journey.
Tracking your diet will help you ensure that you continue to meet your daily recommended nutrient intake.
