Metabolism is the process by which your body converts what you eat and drink into energy. It's a complex chemical reaction that occurs in the body to convert food into energy. The rate at which your body burns calories for energy is called your metabolic rate. This rate can depend on various factors, including age, activity levels, genetics, and other individual characteristics. Understanding how dieting can impact your metabolism and what steps you can take to repair it is essential for maintaining a healthy weight and overall well-being.
Understanding Metabolism
Your metabolism is how your body uses energy for everything it does. This includes basic body functions, like breathing, circulating blood, digesting food, growing and repairing cells, managing hormone levels, and regulating body temperature. It's a continuous process that never stops, even when you’re resting or sleeping. A healthy, life-sustaining metabolism requires cells to function at rest and adapt to a changing environment, including periods of eating, fasting, starvation, physical activity, illness or injury, pregnancy, and lactation.
Metabolic Processes: Catabolism and Anabolism
Metabolism consists of two main processes: catabolism and anabolism.
- Catabolism: The breakdown of macronutrients (carbohydrates, protein, and dietary fats) into their simpler forms. For example, your body breaks down carbohydrates into glucose, which enters your blood as blood glucose (sugar). Your body also stores glucose as glycogen - mainly in your muscles and liver. These macronutrients are the basis of the fuel your body uses for all its cells.
- Anabolism: The opposite of catabolism. Your body takes smaller units (like amino acids) and puts them together to create bigger structures (like proteins). Anabolism is essential when you get an injury, and your body has to heal. It’s also essential for bone growth and building muscles.
Factors Affecting Metabolic Rate
Several factors can affect your metabolic rate, including:
- Age: Metabolism tends to slow down with age.
- Sex: Men generally have a higher metabolic rate than women due to greater muscle mass.
- Body Composition: Muscle mass is a significant factor. The more muscle mass a person has, the higher their metabolic rate.
- Activity Levels: Physical activity increases metabolism.
- Genetics: Genetic factors play a significant role in determining an individual's metabolic rate.
- Diet: The timing of meals and the types of food you eat can affect metabolism.
- Sleep: Insufficient sleep can lower metabolic rate.
- Thyroid Function: Low levels of thyroid hormone can slow metabolism.
The Impact of Dieting on Metabolism
Many people diet or follow restrictive diets to lose weight. However, restrictive diets can sometimes backfire by slowing down your metabolism. When you crash diet, other mechanisms are triggered that make it more likely your metabolism will slow, and you'll regain the weight.
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When your body interprets reduced calorie intake as a threat of starvation, it slows down your basal metabolic rate (BMR), burning fewer calories over time. This is the body's way of conserving energy. Yo-yo dieting, which involves repeated cycles of weight loss and regain, can cause a long-term slowdown in metabolism.
Signs and Symptoms of a Slowed-Down Metabolism
The most obvious signs of a damaged, slow metabolism are weight gain, weight loss plateaus, and difficulty losing weight - even on a low-calorie diet with exercise. Many other signs and symptoms of a slow metabolism mirror those of hypothyroidism.
These include:
- Constipation
- Ongoing fatigue
- Brain fog
- Irritability
- Mood changes
- Erratic or absent menstrual periods
- Muscle loss
- Poor immunity against infection
- Sleep disturbances
- Digestive symptoms such as feelings of intense hunger, heartburn, gas, acid reflux, bloating, and diarrhea.
Why Crash Diets Slow Metabolism
Crash dieting triggers the body to go into starvation mode. Your body protects itself by becoming extremely efficient at absorbing more calories from food. At the same time, your body also deliberately conserves stored energy and burns less of it. It’s a double whammy that results in a slowed metabolism.
Crash dieting also negatively affects your thyroid function. Specifically, it reduces T3 levels, can trigger or worsen hypothyroidism, and further slow your metabolism.
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Other hormones are also affected by rapid weight loss. During and after crash dieting, your stress hormone cortisol increases, creating inflammation, slowing your metabolism, and making your body more effective at storing fat. Rapid weight loss can also cause a leptin drop, -- the hormone that makes you feel full -- or make you resistant to leptin. When you have low leptin or leptin resistance, you feel hungrier and are likely to eat more. Crash dieting can also increase ghrelin levels, the hunger hormone, making you feel hungrier.
Ultimately, researchers have discovered that a crash diet reduces your metabolism far more than slower weight loss. And, after a crash diet, your metabolism stays sluggish, sometimes for years…even if you regain the weight.
Strategies to Repair Metabolism After Dieting
To break the cycle of yo-yo dieting and restore your metabolism to a healthier state, focus on practical ways to increase its speed. Here are some of the best ways to get your metabolism back on track.
Eat Enough Calories and Regularly
Eating too few calories can cause a person’s metabolism to slow down so the body can conserve energy. The Academy of Nutrition and Dietetics advises people to eat regular meals and snacks throughout the day to prevent extreme swings in fullness and hunger. A 2022 study notes that the timing of meals can have an effect on metabolism.
Prioritize Protein Consumption
Reducing calories does not increase the metabolic rate, but modifying the source of calories a person consumes may be a strategy to increase it. Protein, for example, may be more likely than carbohydrates or fat to promote thermogenesis, the burning of calories in the body.
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In a 2019 study, 38 people followed either a high protein diet, with 25% of their calories from protein, or a medium protein diet, with 15% of their energy from protein. Those who consumed a higher proportion of protein burned more energy than those who consumed less. Various experts recommend eating at least 1 gram of protein per pound of body weight daily to support your metabolism.
Optimize Your Thyroid Function
Because crash and yo-yo dieting can trigger hypothyroidism, a thorough thyroid evaluation is essential to your metabolic health. This can pinpoint a previously undiagnosed case of hypothyroidism or identify the less-than-optimal treatment for your current hypothyroidism. It’s helpful to start with a thyroid blood test panel. Ensure the panel includes Thyroid Stimulating Hormone (TSH) and Free T4, Free T3, and Thyroid Peroxidase (TPO) Antibodies. The results will help you understand how your thyroid functions and if it may negatively affect your metabolism.
For those with hypothyroidism, taking medications that increase the levels of thyroid hormone can increase their resting metabolic rate. Seeking help for hypothyroidism can help speed up metabolic rate and reduce the risk of complications linked to this condition.
Eat a Healthy, Nutrient-Dense, Gut-Friendly Diet
After a crash diet or yo-yo diet cycle, you must focus on eating the healthiest, most nutrient-dense diet you can. This means choosing organic, pesticide-free, whole foods as much as possible and avoiding processed foods. Your emphasis should be on fruits and vegetables, healthy fats, good proteins (like fish and grass-fed meats), and anti-inflammatory fermented foods.
You should also pay attention to your gut health. A healthy gut can more efficiently digest and store food, burn energy when needed, and eliminate waste. You may also want to incorporate more spicy foods into your daily diet. Capsaicin, a key ingredient found in some spicy foods like peppers, has been shown to boost metabolism.
Increase Your Fiber Intake
Increasing your fiber intake can help boost metabolism because fiber requires more energy to digest, process, and eliminate. Aim for around 25 grams a day of fiber from foods and fiber supplements. Fiber supplements can help you reach the goal of 25 grams per day.
Eat the Majority of Your Food Earlier in the Day
When you eat also has an impact on your metabolism. Most experts agree that eating a protein-rich breakfast helps stoke and maintain metabolism and promote fat-burning throughout the day. You may also consider making dinner your lightest meal of the day. You can also fast from dinner until breakfast. This helps you maintain healthier leptin levels and gives your body time to access stored energy for your nighttime energy needs.
Stay Well Hydrated
Staying hydrated is essential for the body to function at its best. Water is necessary for optimal metabolism and may help a person lose weight.
You'll want to ensure you regularly drink water throughout the day. Studies have shown that drinking around half of a liter (16 ounces) of water boosts metabolism by up to 30 percent for around 90 minutes. Drinking 2 liters of water daily increases energy expenditure by nearly 100 calories daily. For an extra boost, make it cold water; it raises metabolism a bit more than water at room temperature.
Drink Coffee and Tea
Caffeine can help boost metabolism. One study showed that around 100 milligrams of caffeine - what you'd typically get in a small cup of coffee - could increase your BMR/RMR by about 3 to 4 percent. Several servings of caffeine at intervals throughout the day can boost metabolism by as much as 11 percent. Moderation is needed, however. Going overboard on caffeine can increase insulin resistance and blood glucose levels.
There’s also scientific evidence that various teas - including black, green, oolong, and goji - can slightly increase your metabolism and fat burning. Tea also provides additional hydration, which can help aid in weight loss.
Engage in Strength Training
Lifting weights and performing exercises that use the weight of the body or resistance bands can help build muscle. Building muscle will help you burn more calories even when you’re not moving - and the higher your muscle mass, the stronger your metabolic rate. Strength training may slightly increase a person’s rate of metabolism while resting, for example, when sleeping or sitting. A 2022 review suggests a strong link between high muscle mass and metabolic rates. Eating enough calories - especially protein - can contribute to muscle mass.
Strength training can also help protect your metabolism following a low-calorie diet. One study found that when following a low-calorie diet, women who did resistance training could lose weight without a decrease in metabolism compared to women who did either aerobic or no exercise at all.
Increase Your Activity Level (Carefully)
While intense aerobic exercise might seem beneficial, many metabolism experts recommend avoiding extended periods of it because it raises cortisol levels. Elevated cortisol wreaks havoc on your metabolism, increasing insulin and glucose levels and slowing your metabolism. If you want to do aerobic exercise, shorter periods of intensity - i.e., high-intensity interval training (HIIT) - offer many benefits of aerobic exercise with less risk of raising cortisol.
HIIT training involves very intense bursts of activity. A small 2020 study found that HIIT can indirectly increase metabolism. Specifically, after HIIT, the body burns fat and uses more energy. A 2021 study notes that HIIT can burn more calories than usual after exercise in young, aerobically fit women. Interval training is highly intensive and may be more suitable for people with higher fitness levels than those new to regular exercise.
You can also increase your metabolism by increasing your NEAT. As a starting point, it can be helpful to build regular periods of standing and walking throughout the day.
Get Enough Sleep
Sleep plays an essential role in regulating metabolism, hunger, and appetite. A 2023 study notes that insufficient sleep or sleep disorders can affect the neuroendocrine system, affecting whole-body metabolism. People who have less sleep may have a lower metabolic rate, according to research from 2016. The study took place in a sleep laboratory, and participants slept 4 hours per night for 5 nights, followed by 1 night of 12 hours sleep. Their metabolic rate fell after the nights with little sleep but returned to their usual levels after the night of recovery sleep. The authors believed the body reduces metabolic rate to conserve energy when a person sleeps less. They noted this could lead to weight gain in people who do not get enough sleep.
Getting enough sleep is essential for your metabolism. Experts say that 7 to 9 hours per night should be your objective. "Short sleep" of less than 7 hours contributes to a long list of hormonal changes, including blood sugar and cortisol increases. Short sleep reduces the satiety hormone leptin levels, increases the hunger hormone ghrelin, and increases your risk of insulin resistance. One study found that just five days of short sleep caused an increase in food intake, leading to weight gain. Short sleep also reduces your ability to lose fat. Researchers found that dieters who got only 5.5 hours of sleep over two weeks reduced their fat loss by 55 percent!
Manage Your Stress
The link between stress and the metabolic rate is unclear. An older 2016 study found that chronic stress levels seem to lead to an increase in appetite, food intake, or weight. Authors of a small 2020 study found no evidence linking resting metabolic rate and anxiety. Still, stress could have an indirect effect by affecting eating patterns and sleep, both of which can alter the rate of metabolism.
Active stress management is an integral part of transforming a slow metabolism. Unmanaged stress raises cortisol levels, negatively affecting glucose, insulin, and metabolism. Specifically, chronically high cortisol levels promote abdominal fat storage, contributing to insulin resistance and weight gain.
The key to stress management is devoting at least 10 minutes daily to your stress-reducing activity. What you do to manage stress depends on what methods work best for you. Meditation, breathwork, gentle yoga, tai chi, playing a musical instrument, or needlework are all valid stress-reducing activities. (Note: a daily stress management is also good for your thyroid and immune health!)
Breathe Mindfully
The practice of mindful breathwork has two key metabolic benefits. First, diaphragmatic breathing is a natural stress reducer; a few slow, deep belly breaths can reduce cortisol levels.
Specific breathing techniques have also been studied and shown to help raise metabolism. Yoga practices such as left, right, or alternating nostril breathing can increase oxygen intake and raise metabolism by as much as 37 percent.
Consider Vitamin Intake
Vitamins play an essential role in metabolism. B vitamins are directly involved in the process by which the body uses food calories for energy. The results of a 2018 rodent experiment suggested that a low intake of various B vitamins could affect the rate at which the body metabolizes lipids, including cholesterol and triglycerides. More research may be necessary to understand the relationship between vitamins, metabolism, and weight loss.
Spice Up Your Meals
Some 2016 research has suggested that eating spices such as chili, which contains capsaicin, can increase metabolic rate, including the rate at which the body burns fat and uses energy. However, the Academy of Nutrition and Dietetics says that while eating hot chilies might temporarily boost metabolic rate, it is unlikely to have a significant effect.