How important is fat loss for testosterone optimization

Obesity has been shown to lower testosterone and losing fat can increase testosterone.

A 2013 study found that 32% of men around 45 years of age and 75% of men with severe obesity (BMI > 40 kg/m2) had hypogonadism (R). The largest study evaluating hypogonadism in 2162 males 45 years and older reported that 38.7% were hypogonadal (R, R).

There is this catch-22. Obesity lowers testosterone and low testosterone causes weight gain.

As you can see from the table above, people with a lower BMI (<25) tend to have testosterone over 521ng/dl. It’s still not high, but at least not hypogonadal. If they ate more animal foods and implemented testosterone optimization strategies, their T will likely be >700ng/dl, which is commonly what I achieve with my clients in a couple of weeks.

Being overweight/obese lowers testosterone due to (R):

  • Elevated inflammation
  • Insulin resistance
  • Leptin resistance
  • Drop in SHBG
  • Elevated testicular temperature
  • Sleep apnea
  • Elevated aromatase
  • Gut dysbiosis and an increase in endotoxin production and leaky gut
  • Accumulation of fat-soluble endocrine-disrupting chemicals (R)
  • Abnormally increased expression and activity of enzyme 11b-hydroxysteroid dehydrogenase type 1 (11b-HSD-1) in adipose tissue which activates cortisol. This leads to a high cortisol-to-testosterone ratio.

Clearly, there are many reasons not to gain excess fat in the first place and why it’s also important to get rid of excess fat.

Weight loss and testosterone

Weight loss is associated with an increase in free and total testosterone levels and a decrease in estrogen levels in males with hypogonadism (R). But how significant is the increase in testosterone with fat loss?

How much fat do you have to lose to double your testosterone?

In general (from what studies have found), losing 10% of your body weight will increase testosterone by 3-4nmol/L (87-115ng/dl). So if someone weighs 100kg and loses 10kg, their testosterone will likely go up by 100ng/dl, just due to losing fat. If they optimized their diet and lifestyle as well, testosterone would likely have gone up even more.

Fat loss U-curve

In order to lose fat, your body has to get rid of more calories than what is coming in. You can enhance calories out by moving more, optimizing testosterone, thyroid function and mitochondrial function, etc.

But the biggest factor that will determine fat loss is usually eating less.

That brings us to the energy availability equation. If you create a deficit with food, your body has to use its own resources to survive. If someone has a lot of resources, that’s not a big deal. But the fewer resources someone has, the bigger of a deal it becomes.

The body is constantly partitioning calories for various things.

A common example is exercise-induced hypogonadism; low testosterone due to excessive exercise. Because athletes are so active, the body has less energy for steroidogenesis, so total testosterone drops. However, the body becomes more effective/sensitive to the available testosterone.

Similarly, if someone has a lot of resources and goes into a caloric deficit, testosterone can go up as inflammation and the other bad stuff goes down/away.

However, if someone is already lean and they continue to cut calories, testosterone will take a hit. Natural bodybuilders usually end up with testosterone around 100ng/dl a few weeks before going on stage. Too few calories and too much activity will tank testosterone.

Both obesity and anorexia are non-ideal. No brainer right?

Our goal is to drop to an ideal body fat percentage that will optimize our health and testosterone. Not be extreme to either side.

Let’s look at a few studies.

Study 1

  • Duration: 8 weeks
  • Weight loss amount: mean, 19.5 kg
  • Total calorie intake: 320 kcal/d liquid diet (R)
  • Testosterone increase: 136ng/dl

Despite being in a crazy deficit (starvation diet), all the hormonal levels improved. Most people are not at their ideal weight at 93kg and losing another 10kg which will likely increase their T by another 100 points.

Study 2

  • Duration: 3 months
  • Weight loss amount: 10% of BW
  • Total calorie intake: 1500 ± 200 kcal; 50% carbohydrate, 20% protein, and 30% fat
  • Activity: Brisk walk three times per week for a cumulative time of 150 minutes per week
  • Testosterone increase: only those who lost >10% BW increased T by nearly 100ng/dl (R).

Study 3

  • Duration: 9 weeks
  • Weight loss amount: 16.3kg
  • Total calorie intake: 800 calories
  • Testosterone increase: from 317 to 461ng/dl (144ng/dl increase) (R).

10kg fat loss increases T by about 100ng/dl, which correlates with a drop in inflammatory markers.

Study 4

  • Duration: 17 ±17 months (not a specific set duration)
  • Weight loss amount: 53 ± 36 kg; range, 26-130
  • Total calorie intake: individualized dietary protocols
  • Testosterone increase: 240 ± 116 (8.5 ± 4.0) to 377 ± 113 ng/dL (R)

You can clearly see that hormones improved from obese to reduced obese (before fat loss and after fat loss). Although they made progress, they weren’t at the same levels as normal-weight guys. However, if they continue with the fat loss and reach their ideal weight (same as the normal-weight guys), their testosterone would likely have normalized as well.

Here is 1 guy they follow for 39 months of his fat loss journey. He lost a total of 130kg over this time. His total testosterone more than tripled.

Ketogenic diet, fat loss and testosterone

Some people might wonder if it would be important to have more carbs during fat loss as that might be more advantageous.

Likely not. People on a very low-calorie ketogenic diet also experienced increases in testosterone similar to the other higher-carb groups.

  • Duration: 13.5 weeks
  • Weight loss amount: 21.05 ± 1.44 kg
  • Total calorie intake: The diet consisted of 5 phases. Phase 1: 600–800 calories. Phase 2: 800–1000 calories. Phase 3: 1200–1500 calories. Phase 4 and 5: 1500 and 2000 calories.
  • Testosterone increase: Overweight: 114ng/dl increase. Obese: 116ng/dl increase (R).

Fat loss + aromatase inhibitor on testosterone and hypogonadal symptoms

Study 1: fat loss + 1 mg anastrozole daily

One of the main reasons for low testosterone with obesity is excess aromatase and estrogen. Estrogen inhibits GnRH and LH release from the hypothalamus and pituitary, thus lowering testosterone production. That’s why SERMs like tamoxifen, Clomid, clomiphene, etc, have been created, as it blocks the estrogen receptor in the hypothalamus and pituitary, thus increasing GnRH and LH.

Similarly, lowering estrogen with an aromatase inhibitor (AI) can increase testosterone.

This study did exactly that (R). 2 groups underwent the same fat-loss diet (500–750 calorie deficit with ~1 g of high-quality protein/kg/day) for 6 months. 1 group got an AI (1 mg anastrozole daily) and the other didn’t.

The AI group experienced:

  • Greater increases in total testosterone: 300 vs 500ng/dl – The reason why the regular group didn’t increase T much is because they didn’t lose much fat.
  • Greater fat loss (this was an interesting find. Some people think that estrogen is needed for fat loss in men, but this study throws a spoke in that estro-wheel.)
    • Total weight reduction: 8.3 ± 7.5 kg vs only 3.2 ± 3.8 kg
    • Total fat mass reduction: 4.4 ± 3.9 vs. 0.7 ± 1.9 kg
    • Lean mass loss or retention was the same between the 2 groups.

Interestingly, despite a much bigger increase in testosterone in the AI group, the improvements in hypogonadal symptoms were the same between the 2 groups, likely because estradiol wasn’t excessive to begin with.

Study 2: 2.5mg Letrozole without fat loss

This study is mainly to point out that testosterone optimization (via AI) in the absence of fat loss is unlikely to yield many results.

Letrozole decreased serum estradiol from 119.1±10.1 to 59.2±6.1 pmol/l (P<0.001), and increased serum LH from 3.3±0.3 to 8.8±0.9 U/l (P<0.0001) and serum total testosterone from 8.6±0.7 to 21.5±1.3 nmol/l. Despite a marked rise in serum testosterone, low-dose aromatase inhibition had no somatic or psychological effects in men with OrHH.” (R)

No resolution of hypogonadal symptoms with an AI. Excess estrogen is a symptom of poor diet, lifestyle and obesity. Fixing those will optimize hormonal ratios and get rid of hypogonadal symptoms. Not that I’m saying blocking aromatase should never be done, but likely for most people they need to focus on diet and lifestyle, vs using an AI.

Is it all about fat loss?

To a significant extent yes.

Bariatric surgery is a good example and has been shown to greatly reduce body fat and increase testosterone without subsequent dietary modifications (R). Bariatric surgery is surgery on the stomach and intestines which reduces digestion and absorption of food, thus automatically creating a deficit. Terrible I know. It comes with a lot of side effects.

One case report of someone who got bariatric surgery tripled his testosterone from 4.6 (132ng/dl) to 15.8 (455ng/dl) in 8 months (almost the same results as the guy mentioned above who was in a deficit for 31 months). Keep in mind fat loss occurred during this time and he lost 32% of his BW during this time. Lots of fat loss = a great increase in T.

Why is the increase in testosterone with bariatric surgery more and faster than with fat loss diets?

Because the mean % of body weight loss with bariatric surgery was 32% (as per the study above) as opposed to only 9% on average with diets that aimed to reduce calorie intake. The mean increase in testosterone levels was 9 nmol/L (260ng/dl) in the former and 3-4 nmol/L (86.5 to 115ng/dl) in the latter. The same increase in testosterone levels after bariatric surgery was observed with replacement therapy with gels/patches of testosterone. So we can safely conclude that before proceeding to replacement therapy with testosterone, every effort should be made to lose weight.

In short, fat loss from bariatric surgery is much faster than with diets only. But if the same amount is lost, the increase in testosterone will be the same regardless of the route taken.


Reducing body fat either by diet or bariatric surgery increases testosterone.

Is it enough to increase testosterone high enough and completely resolve hypogonadal symptoms? It depends on your diet and lifestyle habits. If someone is just eating less of their previous shitty diet, then they might experience an increase in testosterone but not complete resolution of their hypogonadal symptoms.

Eat the right foods and you’ll start feeling a lot better much faster.

If you want to rush fat loss on a crash diet (if I was 40kg overweight, would I want to spend the next 3-4 years losing it? NO!), while optimizing your testosterone, here is what I would do.


  • Focus on micronutrient-dense foods – organ meat, oysters, eggs, dairy, etc.
  • Consider protein-modified fasting days.
    • Fasting lowers testosterone, but having enough protein in the diet prevents that (R).
  • Focus on high-satiety foods
  • Implement satiety-promoting activities, such as intermittent fasting, keto, etc.

I would alternate between 2 days.

  • Day 1: Normal-ish diet: 1L 1% milk, 3 fatty lamb chops and 3 large oysters – 1750 calories
  • Day 2: 3 scoops of whey in 3 cups of coconut milk or water – 500 calories

It’s often better for adherence to cycle between a low and a higher-calorie day than just sticking to very low-calorie days.

Tests to do to see if you’re moving in the right direction healthily

  • LH
  • FSH
  • Total and free T
  • hsCRP
  • ESR
  • AST
  • ALT
  • Fasting glucose
  • Fasting insulin
  • C-peptide
  • HbA1c
  • Cortisol
  • Total and free T3

If you need help getting your hormones and body comp back on track, reach out below or book a free call with me.

>1000ng/dl Testosterone: My Step-by-Step Guide on How I Do It Naturally!

3 thoughts on “How important is fat loss for testosterone optimization”

  1. This is some of the best info, I’ve come across. All free, up to date, scientific and understandablr.
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