What’s causing your lethargy, and what can help?

Everyone feels tired from time to time, but if you’re regularly experiencing lethargy or a lack of energy, there are lifestyle changes you can try. You should also consider whether your lethargy is a sign of an underlying health condition.

Lethargy on its own is not an illness, but it may be linked to health concerns such as a thyroid disorder, not having enough iron in your blood, depression, heart disease, or diabetes

If you’re experiencing lethargy along with other symptoms that are not typical for you, talk to your doctor. 

Lifestyle behaviors such as diet, exercise, and sleeping habits can have an impact on your energy levels.

At ZOE, we run the largest nutrition research program of its kind in the world, with over 15,000 participants so far. We know that the foods you eat can impact your lethargy. Picking the best nutrition for your body can make you feel more energetic and less tired.

Take our free quiz to find out more.

Read on to learn about the best ways to boost your energy if you’re feeling lethargic. 

How to boost your energy

Eating the right foods, sleeping properly, and being active can have a big impact on your overall health and your energy levels

Eat the right food for your body

If you find yourself regularly feeling tired or low on energy, consider keeping a log of when this happens. Does it tend to be around the same time each day? Is it mostly after a meal? What foods did you eat? See if there is a pattern.

What and when you eat can have a strong influence on your energy levels. After you eat, your body breaks down the food into glucose, or sugar, to be used for energy

The glucose is absorbed into your blood and causes a rise in blood sugar levels. But not all foods affect blood sugar levels in the same way.

Carbohydrates are the body’s main source of glucose. When you eat complex carbohydrates, such as whole grains, vegetables, fruits, and legumes like lentils and chickpeas, your blood sugar levels rise and fall more gradually. 

When you eat simple carbohydrates, such as soda, sweets, and other ultra-processed foods, you are more likely to experience a sharper rise or “peak,” which can lead to a dip afterward.

A gradual rise and fall in blood sugar is normal. It’s your body’s way of getting energy from the food you eat. 

However, when the changes are not gradual and your body experiences sharp rises or falls in blood sugar, you may feel weak or tired. While this is more common in people who have uncontrolled diabetes, anyone can experience these feelings. 

In one study, people with a diet that caused large spikes and drops in blood sugar reported 26% higher fatigue scores than those who ate a diet that led to gradual increases and falls. 

ZOE scientists discovered that after closely following our personalized nutrition program, around 80% of participants reported having more energy.

Look after your gut

Another way that the food you eat may influence your energy levels is via the makeup of your gut microbiome, the trillions of bacteria and microbes that live in your gut.

These microbes help you digest the food you eat and are also crucial for a strong immune system and your overall health. Having lots of different microbes, particularly beneficial ones, is a sign of a healthy gut microbiome. 

Studies suggest that people experiencing chronic fatigue may have a less diverse gut microbiome with greater numbers of “bad” bacteria — that are linked with inflammation — and fewer “good” bacteria.

Everyone’s microbiome and the way it responds to different foods is unique.

With the ZOE at-home test, you can find out which bacteria you currently have in your gut microbiome. We also analyze how your body responds to food by testing your blood sugar and blood fat responses. 

The ZOE program uses the latest science to help you find the best foods to boost your “good” gut bacteria, reduce the “bad” bugs, and eat what’s best for your body. 

Go to bed earlier

If you’re feeling tired after meals, your sleep habits could be a factor.

ZOE’s latest sleep study — the biggest of its kind — showed that what time you go to bed can have more of an effect on your blood sugar control the next morning than how many hours of sleep you get. 

Our research found that people who went to bed later had worse blood sugar responses after breakfast, even if they slept in and got the same number of hours as other people who went to bed earlier. 

Poor sleep quality and changes to a person’s usual sleep patterns were also linked with worse blood sugar control after breakfast. 

When you're tired, you're more likely to crave sweet foods. A breakfast high in processed or ultra-processed foods — particularly those high in refined sugars, such as sugary cereals, white bread, pastries, or croissants — is more likely to lead to blood sugar spikes and dips. 

Opt for a breakfast with complex carbs, healthy fats, or protein instead to keep your blood sugar levels steady and to avoid post-breakfast lethargy.

Exercise more

Exercising on a regular basis is good for your health, and it can also boost your energy and make you feel less lethargic. 

Even small amounts of exercise, like walking up the stairs or going for a short walk, can help increase your energy levels.

When you exercise, a number of things happen inside your body that help you feel more energetic

The number of mitochondria in your cells — the parts that create energy from food — increase. More mitochondria means a greater energy supply for your body.

Exercising also improves your circulation, which allows your body to use energy more efficiently and helps your mitochondria to function better.

The Physical Activity Guidelines for Americans advise that any physical activity is good and can help reduce the risk of many chronic health conditions, like dementia, heart disease, diabetes, and cancer.

So, as counterintuitive as it may sound, it may be a good idea to get up and move when you're feeling tired.

Other causes of lethargy

Diet, exercise, and sleep are related to energy levels, but sometimes lethargy is caused by other factors. 

If your exhaustion has lasted longer than 2 weeks, it could be a sign of an underlying health condition and you may want to talk to your doctor.

Other possible causes of lethargy include:

  • Thyroid disorders: Either producing too much or not enough of the hormones your body needs. Other symptoms may include mood swings, dry or thin skin, and changes in the menstrual cycle.

  • Iron deficiency anemia: Not having enough iron in your blood. You may also experience shortness of breath, pale or yellow skin, headaches, and other symptoms.

  • Type 1 or 2 diabetes: When your body doesn’t effectively get fuel from food. Symptoms can include frequent urination and thirst, blurry vision, numbness or tingling in the hands and feet, and slow healing of wounds.

  • Heart disease: Blood flow into the heart is interrupted. You may feel chest pain, shortness of breath, nausea, and other symptoms.

  • History of a stroke: Many people who have had a stroke experience long-term fatigue. Talk to your doctor to see what treatment options may be available.

  • Depression: Lethargy, loss of energy, and a lack of interest in things you usually enjoy often accompany the main symptoms of depression. You may also have insomnia or find yourself sleeping more than usual.

Certain medications, such as antihistamines or antidepressants, as well as many narcotics, like hydrocodone or oxycodone, may also cause drowsiness. 

When to seek medical help

Sometimes lethargy is part of a medical emergency and should be addressed immediately. 

Carbon monoxide poisoning is a life-threatening condition that occurs when someone breathes in too much carbon monoxide, an odorless and colorless gas. Carbon monoxide is produced by burning fuel in vehicles, stoves, lanterns, cooking appliances, water heaters, and furnaces. 

Symptoms of carbon monoxide poisoning can include headache, weakness or fatigue, upset stomach or vomiting, chest pain, dizziness, or confusion. 

Carbon monoxide can leak from appliances if they are not in good condition. For safety, install a carbon monoxide detector and make sure your appliances are serviced regularly.

People experiencing a stroke may also show extreme fatigue or weakness. Other symptoms may be confusion, slurred speech, drooping of the face, numbness, the inability to move one side of the body, and vision loss.

Lethargy in an infant requires immediate medical attention and may be a sign of serious illness. If your baby won’t smile or play, stares off into space, or hardly responds to you, call your doctor immediately.

If you or someone you know is lethargic while experiencing confusion or dizziness, blurred vision, bodily swelling, or thoughts of suicide, call for medical help right away.


Lethargy is a feeling of fatigue and lack of energy. A number of medical conditions and medications can make you feel lethargic. 

If your lethargy isn’t due to these, there are lifestyle changes that you can make to boost your energy levels. 

Eating the right foods for you and your gut microbiome, staying active, and going to bed earlier may help you feel more energetic and less lethargic. 

The ZOE at-home test analyzes your gut microbiome, as well as your blood sugar and blood fat levels, to help you find the best foods for your body. 

Take a free quiz to learn more about what you can achieve with the ZOE program.


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