Do you remember your English classes back in high school? The teacher would assign you some droll book to read and warn you of an impending test on said book. The night before the exam, you would sit down and Google as hard as you could to try and find the Cliffs Notes. Upon finding one, you would read through the summaries and hope it was enough to pass the test. This strategy would usually yield mediocre results. A passing grade but nothing too fancy. Sometimes, this strategy would earn you a big old F.
Some science writers never grew out of the Cliffs Notes phase and employ this strategy when reporting on journal articles. They will read through the abstract, the summary of a paper, and base their article on that single paragraph. Just like your high school English tests, these articles end up misinterpreting and misrepresenting the full context of the study.
Enter Dr. Mark Hyman and his latest article,
In the opening salvos of his article he makes the following claim:
He then gives 5 reasons for how sugar kills your sex drive. Let’s review them to see if he was able to make it past the abstracts, shall we?
Claim 1 - Sugar Lowers Testosterone
- In men, insulin resistance brought on by excessive amounts of sugar drives down testosterone
- Decreased muscle mass and more belly fat are repercussions of low testosterone. Excess body fat can increase levels of the hormone estrogen, leading to low sex drive and trouble getting erections.
- In a study published in Clinical Endocrinology, where 74 men of varying ages underwent an oral glucose tolerance test, researchers found glucose (sugar) induces a significant reduction in total and free testosterone (T) levels.
- Imbalanced levels of testosterone in women can reduce desire, increase body fat, lower muscle mass, and create a fuzzy memory.
Here is the cited article - Abrupt decrease in serum testosterone levels after an oral glucose load in men: implications for screening for hypogonadism .
The purpose of this study was to assess if “T measurement should be drawn in relation to food intake or if it should be obtained in the fasting state” when testing for hypogonadism, a condition where the sex glands produce little or no hormones .
Here’s what the study actually said.
74 adult men were examined in this study. Ages ranged from 19–74 years (mean 51.4 ± 1.4) and comprised of fifty-nine (80%) Caucasians, 12 (16%) African Americans, 1 (1%) Asian and 2 (3%) Hispanics. Measures of BMI found that 8 were normal weight, 29 were overweight and 37 were obese subjects. All subjects had gone through puberty and had normal serum levels of prolactin and thyroid-stimulating hormone. Each participant was given a 2-hour oral glucose tolerance test (OGTT) with 75 g of glucose after a 12 hour fast. Blood samples were drawn at baseline and 4 more times every 30 minutes. Free Testosterone levels were calculated using the Vermeulen equation. After the OGTT, it was determined that 42 subjects had a normal glucose tolerance, 22 had impaired glucose tolerance, and 10 were newly diagnosed as type 2 diabetics. Before the OGTT, 8 men had low total Testosterone levels (<9.7 nmol/L, 280 ng/dL) and the other 66 were normal.
So what happened? During the 2 hour test, Total T went down from 475.50 ng/dL to 403.46 ng/dL (normal is 240-1,000 ng/dL) and Free T went down from 10.09 ng/dL to 7.78 ng/dL (normal is 9-30 ng/dL) [4,5]. So while Total T stayed normal, Free T dipped below the ‘healthy’ range. HOLY CRAP SUGAR IS GONNA MAKE ME IMPOTENT! Slow down there buddy, your penis is going to be just fine.
First of all, they used a calculation (Vermeulen) to get the Free T numbers instead of a more accurate test, like the Liquid Chromatography/Tandem Mass Spectrometry (LC/MSMS), so there will be some slight variability in the measurements . Secondly, a drop in testosterone levels postprandial (after a meal) is not abnormal. If Mark had thoroughly read this paper, he would have seen this little tidbit.
Furthermore, no one is going to sit around all day eating glucose (except maybe a hypoglycemic type 1 diabetic). So saying that a slight drop in T levels while taking 75 g of glucose on an empty stomach somehow translates into eating sugar or flour killing your T production is an utterly ridiculous extrapolation to make based off the data in this study.
At the end of the study, the authors concluded that “men who present with signs and symptoms of hypogonadism…should have morning measurements taken in a fasting state to obtain a clearer picture of total T levels. This is particularly important as serum T levels have been shown to transiently fall well below the normal range in approximately 15% of healthy men over the course of a day” [2,10].
Not a single mention of sugar's effects on sex drive was stated anywhere in this paper. Not once. Because that’s not what this paper was investigating.
- Claim 1A - In men, insulin resistance brought on by excessive amounts of sugar drives down testosterone
Putting aside the assumption here that excess sugar causes insulin resistance (overly simplistic, there are many factors at play here) this statement is true-ish. The authors of the paper note that “we, and others, have demonstrated an inverse relationship between testosterone (T) levels and insulin resistance in men with type 2 diabetes and the metabolic syndrome” [2,10,11,12,13,14].
- Claim 1B - Decreased muscle mass and more belly fat are repercussions of low testosterone. Excess body fat can increase levels of the hormone estrogen, leading to low sex drive and trouble getting erections.
This sounds legit, but no citation is given.
- Claim 1C - In a study published in Clinical Endocrinology, where 74 men of varying ages underwent an oral glucose tolerance test, researchers found glucose (sugar) induces a significant reduction in total and free testosterone (T) levels.
True, but as we have seen, he completely misrepresents the study.
- Claim 1D - Imbalanced levels of testosterone in women can reduce desire, increase body fat, lower muscle mass, and create a fuzzy memory.
Again, could be true. No citation was provided. Among all these claims, the larger implication is that sugar consumption is the main factor in all these issues, but the data he provides does not affirm this.
Claim 2 - Sugar Creates Leptin Resistance
- Leptin also monitors sexual behavior. One study in the journal Clinical Endocrinology looked at three groups of men and found those with higher leptin levels—most likely due to leptin resistance—also had significantly higher body mass index (BMI) and lower levels of testosterone.
Here’s the article - Strong association between serum levels of leptin and testosterone in men .
Ok, let’s see if I can follow his logic on this one.
Lots of sugar causes leptin resistance > leptin monitors sexual behavior > leptin resistant people have higher BMI’s and lower testosterone > therefore, sugar causes low testosterone.
A causes B, B causes C, C causes D, so A must directly cause D. That, my friends, is some mental gymnastics. Let’s see what the study said.
58 adult males were selected for this cross-sectional analysis. Group 1 (n=22) all had untreated hypogonadism (serum T lower than 201 ng/dL), Group 2 (n=20) were hypogonadal patients on androgen substitution therapy and had serum T over 864 ng/dL. For this study Group 2 was treated with testosterone or human chorionic gonadotropin. Group 3 (n=16) had no endocrine disorders, received no treatment, and had serum T levels over 864 ng/dL. At the end of the study, the results showed that Group 1, the men with low T, also had the highest leptin levels. In his article Mark asserts that the higher leptin levels in Group 1 are “most likely due to leptin resistance”. If he had read the paper, he would have seen that their increased leptin levels were due to low testosterone, not leptin resistance.
When Mark cites this study as proof that leptin resistance, brought on by excess sugar, causes lower serum T levels he misses the fact that these men already had hypogonadism, meaning they already had lower T levels that could have been brought on by anyone of these factors :
- Concurrent illness
- Cancer treatment
- Concurrent illness
- Inflammatory disease
- Injury to the testicles
- Kallmann syndrome
- Klinefelter syndrome
- Mumps orchitis
- Normal aging
- Pituitary disorders
- Undescended testicles
- Various medications
- Claim 2 – Chronically high leptin levels brought on by excess sugar in the diet causes testosterone levels to drop.
Excess sugar can be a contributing factor to leptin resistance, but the effect of high leptin levels being directly responsible for driving down T levels is not established by this paper. Only an inverse correlation has been shown between serum T levels and leptin. When testosterone was administered in hypogonadal men, leptin went down. Would the inverse be true? Would T levels go down if leptin was administered? Is low T responsible for driving leptin up or are rising leptin levels responsible for driving T down? Those questions, and the question of leptin resistance induced low T, are outside the scope of this paper. Additional studies would be needed to set up causality.
Claim 3 - Sugar Reduces Growth Hormone (GH) Production
- Studies show insulin reduces your body’s ability to make growth hormone (GH), altering testosterone levels and reducing libido.
Time for the breakdown.
First up, the authors note that it is not just insulin but free fatty acids that exert physiological control on growth hormone (GH) release. Which is to say, both high insulin and high free fatty acids (FFA) in the blood will reduce the GH response to Growth Hormone Releasing Hormone (GHRH). In previous studies, the GH response to GHRH was measured by reducing FFA via insulin infusion or by administration of acipimox, an antilipolytic agent that can reduce FFA levels. The researches noticed that the GH response to GHRH was lower in the insulin infusion group than in the acipimox group. The purpose of this trial was to determine to what extent insulin may reduce GH release independent of FFA.
6 obese subjects (4 men, 2 women; age, 30.8 years; BMI, 36.8) and six normal control subjects (4 men, 2 women; age, 25.8 years; BMI, 22.7) were selected. All subjects were in good health: normal endocrine function, normal glucose tolerance, and were taking no medications. Each group underwent three GHRH tests. Test one was an infusion of GHRH with saline and a placebo. Test two was an infusion of GHRH with saline and acipimox. Test three was an infusion of GHRH with insulin and a placebo.
The results showed that the greater the reduction of FFA in the blood, the higher the GH response to GHRH. The GH response was greater in the control group than in the obese group and the authors speculated it was due to their higher circulating insulin levels. The authors also note that “no correlations were found between the GH response to GHRH and blood glucose levels in both the obese and the normal subjects” .
So does Mark’s claim hold up?
- Claim 3 – Insulin reduces your body’s ability to make growth hormone (GH), altering testosterone levels and reducing libido.
Insulin does not reduce your body’s ability to produce GH. High circulating levels of insulin will inhibit growth hormones response to GH Releasing Hormone. So the GH is still being produced but it might not be getting to where it needs to go.
As for decreased levels of GH reducing testosterone levels, I suspect this is true, but no citations were given.
Claim 4 - Sugar Makes You Tired
- A study published in the journal Neuron found amino acids (protein) increase orexin neurons (a neurotransmitter that regulates eating behaviors, wakefulness, and arousal) and boosted alertness. Excessive sugar, on the other hand, decreased orexin, contributing to fatigue and drowsiness.
The article - Activation of central orexin/hypocretin neurons by dietary amino acids 
The first thing to note is that this study was performed in vitro and in animals (mice, rabbits). The data showed that amino acids stimulated the orx/hcrt neurons the most, concentrations of pure glucose inhibited the pathway, and mixtures of AA’s and glucose-stimulated orx/hcrt neurons nearly as much as AA’s alone. The authors point out that there is evidence this system should not be over or under-stimulated as it may lead to depression and anxiety [17,18,19,20]. As with most systems in the body, there is a range this system likes to be kept in which seems to be mediated by consuming meals of mixed macronutrient composition .
- Claim 4 – Lots of sugar decreases orexin which makes you tied and (presumably) not want to have sex.
Is this true? Who knows. These trials were not conducted in humans so at best his claim is a hypothesis, even though he states it as a fact.
Claim 5 - Sugar Triggers Stress & Anxiety
- High insulin levels also exacerbate chronically elevated levels of cortisol, your stress hormone. When the two hormones stay elevated long after they should taper down, they perform as a team to break down muscle mass, store fat, and dampen libido
The article – none!
Not a single citation was given. This claim could very well be true but it’s hard to analyze when Mark does not provide his sources, as he did in the first four claims.
So is sugar the “biggest culprit that continually knocks sex hormones out of balance” ?
Is sugar a potential contributor to a bigger picture that could result in diminished libido?
Probably. But to say it is “the biggest” culprit is utter nonsense.
Here are some things that actually contribute to or cause loss of libido [21,22]:
- Erectile dysfunction (not synonymous with libido loss)
- Performance anxiety
- Medical conditions
- Thyroid disorders
- Blood pressure medication
- Pregnancy and breastfeeding
- History of sexual abuse
- Low self-esteem
- Poor body image
- Relationship issues
My reasoning for writing this article was not to give you a free pass on sugar. I wrote this piece because there are already numerous, scientifically sound reasons to keep your added sugar intake low [23,24]. The pseudoscientific nonsense pushed by Dr. Hyman will only act to muddy the public’s scientific understanding. The fact that this poorly researched article comes from a doctor just adds insult to injury. He, of all people, should know and do better.