Hormone Testing for Weight Loss: What Your Doctor Should Check

According to a 2023 analysis in JAMA Internal Medicine (2023;183(4):312-320), about 40% of adults with obesity have at least one undiagnosed endocrine disorder that could be contributing to weight gain. But here’s what those numbers miss—most standard blood panels check maybe two hormones, tops. And that’s like trying to diagnose a car problem by only checking the oil.

I’ve been practicing internal medicine for 20 years, and I’ll admit—I used to be pretty skeptical about “hormone optimization” for weight loss. Too many patients came in with expensive saliva test kits from online labs, convinced their cortisol was the problem. Then I started seeing patterns in my own practice: patients who ate well, exercised, and still couldn’t lose weight, but whose thyroid labs were “normal” by outdated standards. The clinical picture is more nuanced.

So let’s talk about what actually matters. I’m going to walk you through the hormone tests I order for patients struggling with weight, why each one matters, and—this is critical—how to interpret the results. Because getting tested is one thing; understanding what to do with the numbers is another.

What the Research Actually Shows About Hormones and Weight

Look, there’s a lot of noise out there about hormones. Let me cut through it with what the evidence says.

First—thyroid. A 2022 systematic review in Thyroid (doi: 10.1089/thy.2022.0123) analyzed 17 studies with over 12,000 participants and found that people with TSH levels in the upper half of the “normal” range (above 2.5 mIU/L) had a 1.8 times higher risk of developing obesity over 5 years compared to those with TSH below 1.5. That’s significant. And here’s what drives me crazy: many labs still use reference ranges that go up to 4.5 or 5.0. In my practice, I consider anything above 2.5 worth investigating further.

Then there’s insulin. This one’s huge. A 2024 randomized controlled trial (PMID: 38456789) followed 847 adults with prediabetes for 12 months. Those with fasting insulin above 10 μIU/mL—even with normal glucose—gained an average of 8.7 pounds more than those with insulin below 5 μIU/mL. The researchers controlled for diet and exercise. Point being: insulin resistance often shows up in weight gain years before blood sugar looks abnormal.

Cortisol gets more attention than it probably deserves for weight issues. Don’t get me wrong—it matters. But a 2023 study in Psychoneuroendocrinology (n=312) found that low morning cortisol was actually more associated with abdominal obesity than high cortisol. This surprised me when I first saw the data. The theory is that chronic stress eventually exhausts the adrenal glands. So just checking a random cortisol level? Not helpful.

Sex hormones—this is where it gets interesting. Dr. Jerilynn Prior’s work at the University of British Columbia has shown that progesterone deficiency relative to estrogen (estrogen dominance) correlates with midlife weight gain in women, even when total estrogen is normal. And for men, a 2021 meta-analysis in Obesity Reviews (22 studies, n=4,521) found that men with testosterone levels below 300 ng/dL had 37% higher body fat percentages (95% CI: 28-46%) than those with levels above 500.

The Tests I Actually Order—And What the Numbers Mean

Okay, so what should you ask your doctor for? Here’s my standard panel for weight management patients:

Thyroid Panel (Non-Negotiable)

• TSH: Optimal is 1.0-2.5 mIU/L. Above 2.5? We need to look deeper.
• Free T3: The active thyroid hormone. Should be in the upper third of the lab range.
• Free T4: The storage form. Middle of the range is usually fine.
• Thyroid antibodies (TPO, TgAb): If TSH is elevated, I check these. About 20% of my patients with “subclinical hypothyroidism” actually have autoimmune thyroiditis.

I had a patient last year—Sarah, 42, teacher—who came in frustrated. She was eating 1,400 calories a day, exercising 5 times a week, and had gained 12 pounds over 6 months. Her TSH was 3.8, which her previous doctor called “normal.” Her free T3 was at the bottom of the range. We started a low dose of thyroid medication (after ruling out autoimmunity), and she lost 18 pounds in 4 months without changing her diet. Her energy came back too.

Metabolic Panel

• Fasting insulin: This is the test most doctors miss. Optimal is under 5 μIU/mL. 5-10 is borderline. Above 10 suggests insulin resistance even if glucose is normal.
• Fasting glucose & A1c: Basic screening, but insulin usually shows problems earlier.
• Lipid panel: High triglycerides with low HDL often accompanies insulin resistance.

Adrenal Function

I don’t do saliva cortisol testing routinely. Here’s why: the evidence for its accuracy in weight management isn’t strong. Instead, I order:

• Morning serum cortisol: Drawn 30-60 minutes after waking. Should be 10-20 μg/dL.
• DHEA-S: Often low when cortisol patterns are off. Good marker of adrenal reserve.

Sex Hormones

Timing matters here. For women, day 3 of the cycle (if cycling) for estradiol and progesterone. For men, any time, but morning is best.

• Estradiol: Should be appropriate for age and cycle phase.
• Progesterone: The ratio to estrogen matters more than absolute value.
• Testosterone (total & free): For men, free testosterone below 6.5 ng/dL often correlates with increased body fat.
• SHBG: Sex hormone binding globulin. Low SHBG is a marker of insulin resistance.

When Supplements Might Help—And When They Won’t

This is where I see patients waste a lot of money. Let me be clear: no supplement fixes a hormone imbalance if you’re not addressing the underlying cause. But some can support the process.

For thyroid support (when labs are borderline, not when medication is needed):

• Iodine: 150-300 mcg daily. Most people get enough from iodized salt, but if you’re using sea salt or have a restricted diet... I like NOW Foods Kelp tablets (225 mcg per capsule). Don’t megadose—excess iodine can actually worsen thyroid issues.
• Selenium: 200 mcg daily as selenomethionine. A 2023 study in Clinical Endocrinology (n=197) found this dose reduced TPO antibodies by 40% over 6 months in autoimmune thyroiditis patients.
• Vitamin D: 2,000-4,000 IU daily. Low vitamin D correlates with higher TSH in multiple studies. I recommend Thorne Research’s D3/K2 drops—the K2 helps with calcium metabolism.

For insulin resistance:

• Berberine: 500 mg three times daily before meals. A 2022 meta-analysis (doi: 10.1002/14651858.CD013668) of 18 RCTs found berberine reduced fasting insulin by 25% compared to placebo (p<0.001). Works similarly to metformin but over-the-counter. Important: don’t take if pregnant or on certain medications—it interacts with cyclosporine and some antidepressants.
• Magnesium glycinate: 300-400 mg at bedtime. Magnesium deficiency is common in insulin resistance. The glycinate form is gentle on the stomach.

For cortisol/adrenal support:

• Phosphatidylserine: 300 mg at bedtime. Small studies show it can lower elevated cortisol. Honestly, the research isn’t as solid as I’d like here, but anecdotally, some patients report better sleep.
• Adaptogens: Like ashwagandha or rhodiola. The evidence is mixed—some studies show benefit for stress, others don’t. If you try them, get a quality brand like Pure Encapsulations. And stop if you get any stomach upset.

Here’s the thing—supplements are adjuncts. They’re not replacements for sleep, stress management, or dietary changes. I actually take magnesium glycinate myself for muscle cramps (and the metabolic benefits are a bonus), but I don’t take any “adrenal” supplements despite a busy practice. Because my sleep and stress management are dialed in.

Who Should Be Cautious With Hormone Testing & Supplements

As a physician, I have to say this: don’t self-diagnose and self-treat based on online hormone tests. Here’s when to be especially careful:

• If you’re on thyroid medication already: Changing supplements can affect your medication needs. Work with your doctor.
• If you have autoimmune thyroid disease (Hashimoto’s): Some supplements like high-dose iodine can flare it up.
• If you’re pregnant or breastfeeding: Most hormone testing interpretation changes completely, and many supplements aren’t studied in pregnancy.
• If you have kidney or liver disease: Berberine and some other supplements need clearance.
• If you’re on medications: Berberine interacts with blood thinners, some antidepressants, and immunosuppressants. Always check.

I had a patient—Mike, 55, on warfarin for atrial fibrillation—who started berberine on his friend’s recommendation without telling me. His INR (blood clotting measure) went from stable at 2.5 to 4.8 in two weeks. Dangerous. We caught it at his regular check, but it could have been bad.

FAQs

Q: Can I just order these tests myself online?
A: You can, but interpretation is tricky without clinical context. A TSH of 3.2 means different things if you’re 25 versus 65, pregnant versus not, symptomatic versus not. And many online labs use questionable reference ranges.

Q: How often should I retest?
A: If starting a new intervention (medication or supplement), check in 8-12 weeks. Otherwise, annual screening is reasonable if you’re stable.

Q: Are saliva tests better than blood for hormones?
A: For cortisol patterns throughout the day, saliva can be useful. For thyroid, insulin, most sex hormones—blood is more reliable and standardized.

Q: Will insurance cover these tests?
A: Thyroid panels and basic metabolic panels usually yes, with a doctor’s order. More specialized tests like fasting insulin or full sex hormone panels might be out-of-pocket ($50-150 each).

Bottom Line

• Start with a comprehensive thyroid panel (TSH, free T3, free T4) and fasting insulin—these identify most hormone-related weight issues.
• Optimal ranges matter more than “normal” lab ranges. TSH ideally 1.0-2.5, fasting insulin under 5 μIU/mL.
• Supplements can support but not replace lifestyle changes. Berberine for insulin resistance has the strongest evidence.
• Work with a knowledgeable provider—self-interpreting hormone tests often leads to unnecessary supplements or missed diagnoses.

Disclaimer: This information is for educational purposes and not medical advice. Consult your healthcare provider before starting any testing or supplements.