Metabolism: What It Is and Whether You Can "Boost" It
What metabolism is, what changes it, and what the evidence says about trying to boost it with foods, teas or supplements. Plain language and no hype.
Content last updated . This page has not been medically reviewed.
Overview
"Metabolism" is the word for how your body turns food into energy and uses it. In everyday talk, people usually mean how many calories they use in a day. Scientists call that total daily energy expenditure. This page explains what it is made of, what actually changes it, and whether you can "boost" it. Evidence labels: established, promising but limited, mixed and insufficient evidence.What daily energy use is made of
A review of energy expenditure in humans says total daily energy expenditure is mainly resting energy expenditure, energy used in physical activity, and the thermic effect of food (the energy used to digest food). [1] Energy use varies over life, partly because of changes in body composition, organ size and activity level. [1]NHS describes the basic idea: to stay at around the same weight, the calories your body uses should match what you eat and drink; if they do not match, body weight may change. [2]
What the research shows about "slow metabolism"
| Claim | What the source found | Evidence |
|---|---|---|
| "Metabolism slows in your 30s and 40s." | In a database of doubly labeled water measurements from people aged 8 days to 95 years, energy use adjusted for fat-free mass stayed stable from about 20 to 60 years, then declined in older adults. [3] | Established (one large observational analysis) |
| "Losing weight slows metabolism." | After weight loss, energy use can fall more than expected for the change in body size, and hunger rises. [4] | Established as a known adaptation |
| "A slow metabolism explains my weight." | NIDDK lists health problems that can be involved, including hypothyroidism (an underactive thyroid), Cushing's syndrome and polycystic ovary syndrome. [5] A clinician can check for these. | Established |
Can you "boost" it?
Muscle and activity. Energy use rises with fat-free mass, and exercise during calorie reduction helped preserve fat-free mass in a review of 34 trials (a mean of 0.87 kg more fat-free mass kept than with calorie restriction alone). [3][6] See Activity, strength and keeping muscle.Green tea and "thermogenic" products. NCCIH says the catechins and caffeine in green tea may have a modest effect on body weight. [7] A Cochrane review of green tea preparations in overweight or obese adults found a small, statistically non-significant weight loss that is unlikely to be clinically important. [8] A review of 54 trials of herbal medicines for weight loss concluded there was insufficient evidence to recommend any of them. [9] Evidence label: insufficient evidence for boosting metabolism this way. See the full claim check at Weight-loss supplements, fat burners, detox teas and vinegar.
Meal timing and other popular tips. Proper evidence not found. I searched and read sources on energy expenditure, weight management and intermittent fasting, but found no source supporting claims such as "eating small meals often speeds metabolism" or "certain foods burn fat." The Cochrane review of intermittent fasting found little to no difference in weight loss compared with regular dietary advice (see Eating patterns compared). [10]
Frequently asked questions
Is there a food that speeds up metabolism?
Proper evidence not found in the sources reviewed. Green tea has a modest effect on weight at most according to NCCIH, and a Cochrane review found a small, non-significant change. [7][8]
Does eating more protein raise metabolism?
A review says higher-protein diets are thought to work in part through energy metabolism, appetite and energy intake, and it reports a modest effect on fullness. [12] I did not find a source showing a lasting rise in metabolism from protein. See Appetite, hunger and cravings.
What does "metabolic" mean in "metabolic syndrome"?
It names a group of conditions (such as high blood pressure and a large waistline) that together raise heart and diabetes risk. [13] See Prediabetes, type 2 diabetes and metabolic syndrome.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
When to get help
References
- Energy expenditure in humans: principles, methods, and changes throughout the life course. PubMed record. Annu Rev Nutr 2024. Read 2026-10-22.
- NHS. Understanding calories. Read 2026-10-22.
- Pontzer H et al. Daily energy expenditure through the human life course. Science 2021. Read 2026-10-22.
- Melby CL et al. Attenuating the biologic drive for weight regain following weight loss: must what goes down always go back up? Nutrients 2017. Read 2026-10-22.
- NIDDK. Factors affecting weight and health. Read 2026-10-22 (page last reviewed May 2023).
- Effects of calorie restriction with and without strength, endurance or mixed training on fat-free and skeletal muscle mass in overweight or obese individuals. PubMed record. Diabetes Obes Metab 2026. Read 2026-10-22.
- NCCIH. Green tea. Read 2026-10-22.
- Jurgens TM et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Syst Rev 2012. Read 2026-10-22.
- Effectiveness of herbal medicines for weight loss: a systematic review and meta-analysis of randomized controlled trials. PubMed record. Diabetes Obes Metab 2020. Read 2026-10-22.
- Cochrane review. Intermittent fasting for adults with overweight or obesity. Cochrane Database Syst Rev 2026. Read 2026-10-22.
- US FDA. Tainted weight loss products. Read 2026-10-22.
- Leidy HJ et al. The role of protein in weight loss and maintenance. Am J Clin Nutr 2015. Read 2026-10-22.
- NHLBI. Metabolic syndrome. Read 2026-10-22 (page last updated May 2022).