{"id":29006,"date":"2026-09-24T00:18:07","date_gmt":"2026-09-23T22:18:07","guid":{"rendered":"https:\/\/www.badania-medyczne.pl\/?p=29006"},"modified":"2026-10-20T13:10:26","modified_gmt":"2026-10-20T11:10:26","slug":"tests-before-weight-loss-what-to-check-before-dieting","status":"publish","type":"post","link":"https:\/\/www.badania-medyczne.pl\/en\/tests-before-weight-loss-what-to-check-before-dieting\/","title":{"rendered":"Tests before weight loss: what to check before starting a calorie-restricted diet"},"content":{"rendered":"

Most people start losing weight through diet and exercise, and only have tests when their weight stops falling. The order should be reversed. Blood tests before weight loss answer three questions: whether there is a medical cause of excess weight that needs treatment (because without it, the diet will not work), whether it is safe for your body to be in a calorie deficit, and what your baseline is, against which progress can be compared after 3 and 6 months. A clinical dietitian will request these tests at your first appointment anyway; bringing your results with you shortens the wait for a meal plan by several weeks. The result report is issued in Polish.<\/p>\n

Tests that explain why your weight is not falling<\/h2>\n

TSH, FT4, anti-TPO<\/h3>\n

Hypothyroidism slows your metabolism, causes water retention and leaves you with less energy for physical activity. It is common, especially in women, and can be treated effectively. TSH is a screening test; FT4 shows whether hypothyroidism is overt, while anti-TPO points to Hashimoto’s thyroiditis. Without bringing thyroid function under control, even a well-planned weight-loss programme produces poor results.<\/p>\n

Glucose, insulin, HOMA-IR, HbA1c<\/h3>\n

Insulin resistance is a condition in which cells respond poorly to insulin, the pancreas produces more of it, and high insulin levels promote fat storage and make it harder to burn fat. Fasting glucose and insulin measurements allow the HOMA-IR index to be calculated. Glycated haemoglobin (HbA1c) shows average blood glucose over 3 months and detects prediabetes. For people with insulin resistance, diets with a lower glycaemic load and strength training are more effective; this changes the strategy, so it is worth knowing at the outset.<\/p>\n

Lipid profile<\/h3>\n

Total cholesterol, LDL, HDL and triglycerides (optionally non-HDL and ApoB). High triglycerides with low HDL are a typical pattern in metabolic syndrome. A lipid profile before dieting and after 3 months is the best evidence that lifestyle changes are working, and is more motivating than the scales.<\/p>\n

Serum cortisol<\/h3>\n

Chronic stress and insufficient sleep raise cortisol, which promotes abdominal obesity and bouts of hunger. A morning blood cortisol test provides an initial indication; if Cushing’s syndrome is suspected, your doctor will request dynamic tests. It is worth measuring when fat accumulates mainly around the abdomen and the back of the neck, and stretch marks, hypertension and insomnia are present.<\/p>\n

Prolactin, sex hormones<\/h3>\n

In women with irregular menstrual cycles, acne and male-pattern hair growth, PCOS needs to be ruled out (testosterone, SHBG, DHEA-S, LH, FSH). Men with abdominal obesity and reduced energy often have low testosterone, creating a vicious circle: obesity lowers testosterone, and testosterone deficiency promotes obesity.<\/p>\n

Safety checks before a calorie deficit<\/h2>\n

Full blood count, ferritin, vitamin B12, folate (folic acid)<\/h3>\n

A calorie deficit means less food, and therefore less iron and fewer vitamins. Someone starting a weight-loss diet with low ferritin will quickly develop anaemia, which saps the energy needed for exercise and increases appetite. It is worth correcting deficiencies before starting the diet or alongside it.<\/p>\n

Vitamin D<\/h3>\n

Obesity is associated with lower 25-OH-D levels (the vitamin dissolves in fatty tissue). Deficiency reduces muscle strength and worsens mood, while supplementation is inexpensive and safe when levels are monitored.<\/p>\n

Liver function tests: ALAT, ASPAT, GGT<\/h3>\n

Most people with abdominal obesity have fatty liver disease. Raised ALAT and GGT before dieting are a reason to limit fructose and alcohol; their return to normal after a few months is one of the earliest effects of weight loss. Very rapid weight loss (more than 1\u20131.5 kg per week) can temporarily worsen liver function test results and promote gallstones, so monitoring during the process makes sense.<\/p>\n

Creatinine, eGFR, uric acid, electrolytes<\/h3>\n

High-protein and ketogenic diets put a strain on the kidneys and raise uric acid; they need to be modified for people with gout or kidney disease. Sodium and potassium matter when following low-carbohydrate diets, which increase the excretion of water and electrolytes (hence the \u201cketo flu\u201d).<\/p>\n

Urinalysis<\/h3>\n

An inexpensive test that detects proteinuria, glucose in the urine and ketones, as well as urinary tract infections, which are more common in diabetes.<\/p>\n

How to use the results<\/h2>\n\n\n\n\n\n\n\n\n\n
Result<\/th>\nWhat it changes in your weight-loss plan<\/th>\n<\/tr>\n<\/thead>\n
Raised TSH<\/td>\nthyroid treatment first, then diet; recheck TSH after 6\u20138 weeks<\/td>\n<\/tr>\n
High insulin, HOMA-IR<\/td>\nlower glycaemic load, regular meals, strength training and possibly medical treatment<\/td>\n<\/tr>\n
Low ferritin, B12<\/td>\nsupervised supplementation, a diet rich in iron and B12, repeat testing after 3 months<\/td>\n<\/tr>\n
High ALAT, GGT<\/td>\nlimit alcohol and fructose, keep weight loss to 0.5\u20131 kg\/week<\/td>\n<\/tr>\n
High uric acid<\/td>\ntake care with high-protein diets and fasting, drink plenty of fluids<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

When to repeat the tests<\/h2>\n

After 3 months: lipid profile, glucose, insulin, liver function tests, full blood count and ferritin (if it was low at baseline). After 6\u201312 months, the full set. If you are taking medicines to support weight loss (e.g. GLP-1 analogues), your doctor will set an individual monitoring schedule. Results should be interpreted by a doctor or clinical dietitian; this article does not replace a consultation.<\/p>\n

Preparing for the tests<\/h2>\n

Have the tests in the morning, on an empty stomach (12 hours without food), after a good night’s sleep, with no alcohol for 3 days and no intense exercise the day before. In the preceding days, eat your normal diet, without fasting or \u201ccleanses\u201d, which will distort glucose, insulin and lipid results. Cortisol and prolactin tests require 30 minutes of rest before blood collection.<\/p>\n

\n

Starting to lose weight or work with a dietitian? Have baseline tests without a referral; the results will be useful at your first appointment:<\/strong><\/p>\n