You are eating well. You are training. The weight is not shifting. Before you cut more calories or add more cardio, check whether your biochemistry is working against you. Six systems determine whether your body burns fat or holds onto it.
If you are in a genuine calorie deficit and not losing weight, at least one of these systems is likely working against you. A comprehensive blood test identifies which one.
Your thyroid sets your metabolic rate. If Free T3 (the active hormone) is low, your body burns fewer calories at rest, during exercise, and during digestion. Subclinical hypothyroidism, where TSH looks "normal" but Free T3 is suboptimal, can account for 3 to 5 kg of unexplained weight and make further loss extremely difficult. Most GPs only check TSH. If TSH is normal, you are told your thyroid is fine. Without Free T3 and thyroid antibodies, a conversion problem or early Hashimoto's is invisible. Thyroid testing guide.
Insulin is the master switch between fat storage and fat burning. When your cells are insulin resistant, your pancreas produces more insulin to compensate. High circulating insulin actively inhibits fat breakdown (lipolysis), promotes fat storage (lipogenesis), drives hunger and carbohydrate cravings, and reduces the effectiveness of calorie restriction. You can be in a deficit and still not lose fat because elevated insulin is blocking the metabolic pathway. Fasting insulin and HOMA-IR reveal this. HbA1c and glucose do not catch it until years later. Metabolic testing guide.
Chronic cortisol elevation promotes visceral fat storage (particularly abdominal), increases appetite, drives cravings for high-calorie foods, impairs sleep quality, breaks down muscle tissue (reducing metabolic rate), and worsens insulin resistance. Cortisol is the reason stress makes you gain weight around your middle even when your diet has not changed. Testing cortisol alongside DHEA-S reveals whether your stress axis is driving fat storage.
Low testosterone in both men and women reduces muscle mass, lowers metabolic rate, and shifts body composition toward fat. In women, PCOS-driven androgen excess causes insulin resistance and central fat deposition. Oestrogen dominance (high oestrogen relative to progesterone) promotes fluid retention and fat storage. SHBG determines how much of your sex hormones are actually bioavailable. Without the full hormonal picture, you are guessing. Hormone testing guide.
Systemic inflammation disrupts leptin signalling (the hormone that tells your brain you are full), worsens insulin resistance, impairs mitochondrial function, and promotes fluid retention that masks fat loss on the scale. hs-CRP quantifies this. An hs-CRP above 3.0 mg/L alongside a weight loss plateau suggests inflammation is a contributing factor. Dietary triggers, poor sleep, and gut dysfunction are common drivers.
Low vitamin D is associated with increased fat storage and impaired fat metabolism. Low iron causes fatigue that reduces activity levels and exercise intensity. Low B12 impairs energy metabolism. Low magnesium affects sleep quality and insulin sensitivity. These deficiencies are common, compound each other, and quietly sabotage weight loss efforts even when diet and exercise are on point. Vitamin testing guide.
The point of testing is not just knowing what is wrong. It is knowing what to do differently.
If Free T3 is low, address conversion first. Iron, selenium, and stress reduction support T4-to-T3 conversion. If antibodies are positive, discuss treatment with your GP. Optimising thyroid function can restore 100 to 300 calories per day of metabolic rate.
Shift from calorie counting to carbohydrate management. Prioritise protein and fibre. Add resistance training (builds insulin-sensitive muscle tissue). Consider time-restricted eating. Your report gives specific HOMA-IR-based recommendations.
More exercise and fewer calories will make cortisol worse, not better. Prioritise sleep, reduce training volume temporarily, manage psychological stress, and ensure adequate caloric intake. Counterintuitive, but cortisol-driven fat storage responds to recovery, not restriction.
Low testosterone responds to sleep, resistance training, stress reduction, and body fat reduction (which itself requires addressing the other blockers first). PCOS-driven weight gain requires insulin management as the primary intervention. Your report identifies the specific hormonal pattern.
Identify and remove dietary triggers (common ones: gluten, dairy, seed oils, alcohol). Prioritise omega-3 intake. Improve sleep quality. Address gut health. Inflammation-driven weight resistance often breaks rapidly once the trigger is removed.
Supplement what is actually low, at the right dose, in the right form. Your report gives specific recommendations. Correcting vitamin D alone can improve insulin sensitivity and energy levels within 6 to 8 weeks.
A blood test identifies biochemical blockers. It does not replace the fundamentals. If your diet is genuinely in a significant surplus, no amount of thyroid optimisation will cause weight loss. If you are sedentary, correcting insulin resistance will help but will not do the work for you.
The value of testing is for people who are already doing the right things and not seeing results, or who want to understand which specific adjustments will have the biggest impact. It turns guesswork into data-driven decisions.
Your TrueVitals report cross-references your biomarkers with your lifestyle quiz data (exercise habits, dietary patterns, sleep quality, stress levels, symptoms) to give you recommendations that account for both your biochemistry and your behaviour. See how our reports work.
Full thyroid (TSH, FT3, FT4, antibodies), fasting insulin and HOMA-IR, testosterone and SHBG, cortisol and DHEA-S, hs-CRP, HbA1c, vitamin D, B12, full iron studies, and liver function (ALT, GGT for fatty liver screening). TrueVitals Ultimate (114 markers, £349) covers all of these and more.
Yes, if a biochemical blocker is contributing to your plateau. Thyroid dysfunction, insulin resistance, cortisol elevation, hormonal imbalance, inflammation, and nutrient deficiencies all impair fat loss. Identifying and addressing the specific blocker can break a plateau that willpower alone cannot. A blood test turns guesswork into targeted intervention.
Your GP may test TSH if you describe weight gain alongside other thyroid symptoms. If TSH is normal, further testing is unlikely. Free T3 and thyroid antibodies, which catch conversion problems and early autoimmune thyroid disease, are rarely tested through the NHS. A private comprehensive panel tests the full thyroid picture. Thyroid testing guide.
Before is ideal. It establishes your baseline and identifies blockers that could prevent your diet from working. Testing after 3 to 6 months of dietary changes shows what has improved and what still needs addressing. Both are valuable. If you are already dieting and stalled, test now to find out why.
Yes. GLP-1 medications are powerful but they do not address underlying thyroid dysfunction, nutrient deficiencies, or hormonal imbalances. Comprehensive testing alongside GLP-1 use ensures you are not losing muscle alongside fat (testosterone, SHBG), your thyroid is functioning optimally, your nutritional status is maintained, and your metabolic health is genuinely improving, not just producing weight loss on the scale.
Thyroid, insulin, hormones, cortisol, inflammation, and nutrients. 114 biomarkers. AI-powered analysis. Targeted recommendations. £349.
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