What Increases Mitochondria? Exercise, Fasting & More

Mitochondria are the tiny structures that turn food and oxygen into the energy your cells run on, and your body adds more of them when it is asked to work harder. Exercise is the one approach with strong evidence for increasing them in people.¹ Most of the excitement about fasting, cold plunges, and anti-aging pills comes from mice and lab dishes, not from people. More mitochondria is also not the only win, because training can make the ones you already have bigger and better at their job.²

How Your Body Decides to Build More Mitochondria

When muscle cells burn through energy faster than they can replace it, an energy sensor switches on.³ That sensor then turns up a protein called PGC-1α, which researchers call the master switch for building mitochondria.⁴ The master switch coordinates the genes that assemble new energy machinery and help cells burn fat.⁵ A related signal involving the molecule NAD+ also activates it, which is why many supplements target that route.⁶

Short, repeated bouts of energy stress tell the body to prepare for more of the same, the way muscles grow after lifting. Stress that never lets up, like chronically poor sleep, has the opposite effect.

Building mitochondria needs two sets of instructions. Mitochondria descend from bacteria and still carry a tiny genome of their own, with only 37 genes.⁷ Most of the parts they need are made from instructions in the cell’s main DNA.⁸

Building is balanced by cleanup. Cells constantly clear out worn-out mitochondria while making fresh ones.⁹ The same stresses, like exercise, often trigger both cleanup and building at once.¹⁰

Number, size, and how efficiently each one works are separate things. A muscle can improve its energy output without adding any new mitochondria.

Exercise Is the Proven Way to Increase Mitochondria

Across many human studies, regular training raised muscle mitochondrial content by about 20 to 30%.¹¹ Steady endurance training gave about a 23% gain, while high-intensity and sprint intervals gave about 27%.¹² For scale, untrained muscle is about 2 to 6% mitochondria by volume, and trained athletes reach about 11%.¹³

Some of the gain is bigger mitochondria, not more of them. In one training study, mitochondrial volume in muscle rose 55% while the number of mitochondria stayed the same.¹⁴ In that study, though, the muscle’s maximum energy-making capacity did not change.¹⁵

Intervals have a small edge. Compared directly, high-intensity intervals raised a key mitochondrial enzyme more than moderate steady cardio did.¹⁶ Another measure of mitochondrial function rose about equally with both.¹⁷

Zone 2 training means easy exercise you can sustain while talking comfortably. The claim that it is the best intensity for mitochondria comes mostly from elite athletes who train many hours a week.¹⁸ For most people, the evidence does not support Zone 2 as the optimal intensity, and harder efforts work at least as well.¹⁹

A practical week mixes two or three steady sessions with one or two interval sessions. Intervals can be as simple as alternating fast and easy minutes on a bike. If you’re short on time, they give comparable gains in less of it.

Changes build over weeks of regular training, not days, and they fade if you stop. Beginners usually see the biggest relative change.

Weight Training Boosts What Your Mitochondria Can Do

After a program of resistance training, muscle’s maximum mitochondrial energy capacity rose about 65%.²⁰ Yet twelve weeks of heavy lifting improved energy output with only a small change in the amount of mitochondria.²¹

Light weights can work too. Both heavy lifting and light lifting with a cuff that restricts blood flow sped up the building of mitochondrial proteins equally.²² People who can’t lift heavy may therefore still get this benefit. Cuff training should be learned from a trained coach or therapist.

Cardio and lifting complement each other: cardio adds mitochondrial content while lifting improves how much those mitochondria can deliver. Doing both covers both kinds of improvement, and two strength sessions a week fit alongside cardio for most people. Lifting also preserves the muscle tissue that mitochondria live in.

Fasting and Keto Have Early but Limited Evidence

Fasting effects come mainly from mice. In mice on a high-fat diet, intermittent fasting raised NAD+ and a mitochondrial protein in fat tissue.²³ That was fat tissue in mice, not human muscle. Fasting may support mitochondria, but there’s no human proof yet that it adds them.

Keto has stronger animal data, but only in muscle. One month of a ketogenic diet increased the number of mitochondria in leg muscle of middle-aged mice.²⁴ The same diet did not change mitochondria in the brain or liver.²⁵ Mice kept on keto for 14 months still showed muscle mitochondrial gains.²⁶

In people, keto seems to change how mitochondria work. In people combining keto with exercise, muscle mitochondria produced about 36% more energy when burning fat.²⁷ That came alongside weight loss, so the diet alone can’t take all the credit.²⁸ Keto also appears to help aging muscle more than it helps athletes perform.²⁹ A change in one tissue doesn’t mean the whole body changes, so treat these results as promising leads, not settled advice.

If you try keto or fasting, pick it for reasons like weight or blood sugar, not mitochondria alone. Pair it with exercise, which has the stronger evidence. And check with a doctor first if you take diabetes or blood pressure medicines.

Heat Has Human Evidence and Cold Mostly Animal Evidence

Heating a leg muscle 2 hours a day for 6 days raised the master switch and mitochondrial energy capacity in people.³⁰ Heat also triggers signals for new blood vessels, better blood sugar control, and muscle growth.³¹ And daily heat helped protect muscle mitochondria during a week of limb immobilization.³² That suggests heat may help most when you can’t exercise, such as during injury recovery.

Those studies used targeted muscle heating, not standard saunas. A sauna raises body temperature broadly and calls for plenty of water. If you have a heart condition or are pregnant, get medical advice before using heat. Heat supplements exercise rather than replacing it.

Cold works on brown fat in animals. Brown fat is a type of fat that burns energy to make heat. Three days of cold raised mitochondria in brown fat of mice, even while old ones were being cleared.³³ Prolonged cold also built more internal folds in brown-fat mitochondria.³⁴ Adults have little brown fat, so these findings may not apply much to people.

Brief plunges differ from the days of cold used in mice, and any mitochondrial benefit in people is unproven. Cold water also carries risks, like cold shock for people with heart problems.

Supplements Are Backed Mainly by Lab and Animal Studies

NAD+ is a molecule cells need to make energy, and its levels fall with age. NMN and NR are supplements that the body turns into NAD+.³⁵ In mice, worms, and cells, they improved mitochondrial function and growth.³⁶ Long-term NMN slowed age-related decline in mice.³⁷ But these results are from animals and cells, not people.³⁸

Plant compounds follow a similar pattern. Quercetin, found in onions and apples, increased mitochondria in muscle and brain of mice, and those mice could run longer.³⁹ Resveratrol activated the master switch in mouse liver and muscle.⁴⁰

When a label cites mitochondria, it usually leans on animal studies. Doses in mice don’t translate simply to human pills. Supplements are not checked for effectiveness before sale, and it’s worth asking a doctor before combining them with medicines. Eating fruits and vegetables delivers these compounds safely, and exercise raises the same signals the pills target.

Metformin and Other Medicines

Metformin, a common diabetes drug, improved mitochondrial function in blood cells of people with type 2 diabetes.⁴¹ In mice, it raised mitochondrial density only when the cell’s energy sensor was present.⁴² In healthy mice, two weeks of metformin did not change muscle mitochondrial function.⁴³

Benefits appear in people with diabetes, not healthy users, and it may blunt some exercise gains. Only take it with a prescription.

What Lowers Mitochondria, Sleep Loss, Aging, Diabetes, Altitude

Across species, missing sleep disrupts mitochondria, especially in the brain.⁴⁴ Sleep loss raises harmful byproducts that damage mitochondria and cut energy supply.⁴⁵

Aging muscle builds new mitochondria less readily in response to training.⁴⁶ How much less is still debated.⁴⁷ Exercise still improves mitochondria in older adults, though gains may be smaller. People with type 2 diabetes have smaller, less capable muscle mitochondria,⁴⁸ and insulin resistance links to fewer, smaller mitochondria.⁴⁹ After 66 days at very high altitude on Everest, muscle mitochondria fell 21%.⁵⁰

For sleep, adults should aim for seven to nine hours. Recovery days help training gains, and hard training without enough sleep undercuts itself.

How to Tell if Your Mitochondria Are Improving

Researchers measure mitochondria by taking small muscle samples and examining them under a microscope.⁵¹ Fitter people in one study had muscle that was 4 to 15% mitochondria.⁵² Home tests claiming to measure mitochondria are unreliable.

Practical signs are easier to track: breathing more easily at the same pace, recovering faster between intervals, and a lower resting heart rate over months. A fitness watch’s VO2 max estimate trending upward is one rough clue among several, since these estimates can be imprecise.