Insulin resistance in the lean: prevention, diagnosis and when to see a doctor
A person of normal weight rarely thinks about checking carbohydrate metabolism, and doctors do not always offer such tests. As a result, insulin resistance and prediabetes in lean people are detected late. The editorial team explains which tests are really informative, how an athlete should prepare for them properly, what works for prevention, and at what signs a consultation with an endocrinologist is needed.
Who should get checked
The guidelines of the American Diabetes Association (ADA) recommend screening for prediabetes and diabetes in all adults from age 35, and earlier in the presence of risk factors. These factors also concern people of normal weight: type 2 diabetes in first-degree relatives, a history of gestational diabetes, polycystic ovary syndrome, raised blood pressure, dyslipidaemia, low physical activity.
For people with a normal BMI, waist circumference is especially important. An increased waist at normal weight indicates an excess of visceral fat. A waist-to-height ratio above 0.5 is often used as a simple guide for assessing cardiometabolic risk.
Among athletes and people who train actively, reasons for examination may be prolonged use of glucocorticoids, non-medical use of growth hormone or anabolic steroids, as well as a sharp cessation of training after a long career while maintaining a high-calorie diet.
Finally, signs that may indicate insulin resistance: dark velvety patches on the neck and in the armpits (acanthosis nigricans), raised triglycerides with low HDL, fatty liver disease on ultrasound, and in women — cycle disorders and signs of hyperandrogenism.
- Type 2 diabetes in parents or siblings.
- Increased waist circumference at normal weight.
- Raised triglycerides, low HDL, fatty liver.
- Polycystic ovary syndrome, a history of gestational diabetes.
- Prolonged intake of glucocorticoids or hormonal drugs.
Tests: what each one shows
Fasting glucose is a basic but low-sensitivity test: in insulin resistance it remains normal for a long time thanks to a compensatory rise in insulin. By ADA criteria, values of 5.6–6.9 mmol/L correspond to impaired fasting glucose, and from 7.0 mmol/L (on repeat confirmation) — to diabetes.
Glycated haemoglobin (HbA1c) reflects average glucose over 2–3 months. By ADA criteria 5.7–6.4% corresponds to prediabetes, 6.5% and above — to diabetes. In athletes with anaemia, altered red-cell turnover or after blood loss, HbA1c may be inaccurate.
The oral glucose tolerance test (OGTT) with 75 g of glucose is the most sensitive to early disorders. A glucose level after 2 hours of 7.8–11.0 mmol/L means impaired tolerance, 11.1 and above — diabetes. At the doctor’s decision, insulin is also measured during the test.
Fasting insulin and the HOMA-IR index give an indirect assessment of insulin resistance. However, the methods of measuring insulin are not fully standardised, and the HOMA-IR thresholds differ in different populations. So this index is useful for tracking dynamics and for research, but is not a standalone diagnosis.
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting glucose, mmol/L | < 5.6 | 5.6–6.9 | ≥ 7.0 |
| HbA1c, % | < 5.7 | 5.7–6.4 | ≥ 6.5 |
| Glucose 2 h after OGTT, mmol/L | < 7.8 | 7.8–11.0 | ≥ 11.1 |
The thresholds in the table are given by ADA criteria; a diagnosis of diabetes requires confirmation by a repeat test if there are no clear symptoms of hyperglycaemia.
How an athlete should prepare
Intense or prolonged training the day before can temporarily change insulin sensitivity and glucose level. For the result to reflect the usual state, on the day before the test it is better to limit yourself to light exertion, and to do a hard workout at least a day or two before the blood draw.
Before an OGTT, a usual, not low-carbohydrate diet is needed for several days. After a prolonged keto diet or fasting the body responds worse to a glucose load, and the test may falsely show impaired tolerance.
The test should not be taken during an acute illness, after a sleepless night or during a period of a very strict calorie deficit before competitions. The doctor should be told about all drugs and supplements, especially glucocorticoids, growth hormone, anabolic steroids and beta-agonists.
The result of a single test is only a snapshot. If the value is borderline, the doctor usually recommends repeating the study or performing an OGTT. You should not diagnose yourself using a HOMA-IR calculated online.
Prevention: what gives the greatest effect
Regular physical activity is the basis of prevention. In the Diabetes Prevention Program study, lifestyle change (physical activity of about 150 minutes per week and moderate weight loss) reduced the rate of progression from prediabetes to diabetes by 58% — more than metformin. Although the participants were overweight, the principle of how training works is universal.
For lean people strength training is especially important: increasing muscle mass raises the body’s capacity to utilise glucose. Combining strength and aerobic exercise gives the best effect. Even short walks after eating lower postprandial glucose rises.
In nutrition, whole-grain products, legumes, vegetables, adequate protein and dietary fibre, and limiting sugary drinks and refined carbohydrates are useful. For people of normal weight the goal is not weight loss but reducing visceral fat and improving body composition.
No less important are sleep (regular sleep deprivation lowers insulin sensitivity), stress management and quitting smoking. It is also important to avoid non-medical use of growth hormone, glucocorticoids and other drugs that worsen carbohydrate metabolism.
When to see a doctor
You should see an endocrinologist or therapist if tests showed prediabetes, if there are several risk factors, if a woman has a disturbed menstrual cycle with signs of androgen excess, or if dark patches have appeared on the skin of the neck and in the armpits.
You should seek help urgently with symptoms of marked hyperglycaemia: severe thirst, frequent urination, unexplained weight loss, weakness, the smell of acetone on the breath, nausea. In lean people such symptoms may indicate not type 2 diabetes but autoimmune diabetes (type 1 or LADA), which requires insulin.
Emergency care is also needed for signs of hypoglycaemia — trembling, sweating, confusion, convulsions. Hypoglycaemia during the non-medical use of insulin is especially dangerous: it can be fatal. In such a case call an ambulance immediately and tell the medical staff about the drug.
Treatment of insulin resistance and prediabetes is primarily non-drug. Metformin and other drugs are prescribed by a doctor when indicated; taking them on your own “for insulin sensitivity” without an examination is not recommended.
Editorial conclusions
Normal weight does not exempt you from checking carbohydrate metabolism: waist circumference, family history, lipids and liver condition help to assess risk.
The most informative tests are fasting glucose, HbA1c and the glucose tolerance test; HOMA-IR is useful as an auxiliary indicator. It is important for athletes to prepare properly so that training or diet do not distort the result.
Strength and aerobic training, quality nutrition, sleep and giving up dangerous pharmacology are the most effective prevention.
We also recommend reading our materials on the causes of insulin resistance in lean athletes, on interpreting a biochemical blood test and on the risks of non-medical use of insulin.
References
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S20–S42.
- Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002;346(6):393–403.
- Matthews DR, Hosker JP, Rudenski AS, et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia. 1985;28(7):412–419.
- Katz A, Nambi SS, Mather K, et al. Quantitative insulin sensitivity check index: a simple, accurate method for assessing insulin sensitivity in humans. J Clin Endocrinol Metab. 2000;85(7):2402–2410.
- Stefan N. Causes, consequences, and treatment of metabolically unhealthy fat distribution. Lancet Diabetes Endocrinol. 2020;8(7):616–627.
- Ruderman N, Chisholm D, Pi-Sunyer X, Schneider S. The metabolically obese, normal-weight individual revisited. Diabetes. 1998;47(5):699–713.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
