Low Carbohydrate Diets and Men's Cortisol and Testosterone

Do Carbs Lower Cortisol?

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.


A low carb diet involves replacing common starches and sugars with fats and proteins instead, often in an attempt to reduce fat.

Recent research revealed that following a low-carbohydrate diet could negatively influence men's cortisol and testosterone levels.

The investigation reviewed 27 intervention studies which compared an LCD (35% of energy from carbohydrates) with a HCD (39% of energy from carbohydrates) among 309 men.

Carbohydrates Explained

Carbs may get a bad rap, but they serve a vital purpose in our diets. Along with fat and protein, carbohydrates provide your body with energy.

Your digestive system breaks down carbohydrates into blood glucose that provides energy to power its functions; too many carbs could increase this level too much and increase your risk for diabetes.

Monosaccharides, or single sugar molecules, are the simplest carbohydrates.

Their general chemical formula is (C*H2O)n where n is the number of carbon atoms.

One such monosaccharide is glucose with its formula C6H12O6, chemical structure shown below and two oxygen atoms bound to one carbon atom at an asymmetric center.

Additionally there are six hydroxyl groups giving this sweet tasteful molecule its sweet taste as well as being an important building block in nucleic acids

Monosaccharides can also be combined into disaccharides, or double sugar molecules.

Maltose and lactose are two commonly encountered disaccharides with chemical formulae of C6H12O6 and C4H12O6, respectively.

Maltose has six carbon atoms with four hydroxyl groups while lactose contains five carbons with two. Carbs serve not only as energy sources but are vital components of human tissue as they fuel plant, animal, and human cells alike.

Carbs play an essential role in brain activity, providing energy for nerve cell activity and aiding memory, learning and thought processes.

Carbs also serve to prevent muscle fatigue during physical exercise by providing steady energy streams to working muscles; furthermore they support fat metabolism and can even regulate your blood pressure.

Sources of Carbohydrates

Good carbohydrates come from whole food sources like fruit, vegetables, milk and starchy vegetables such as potatoes, corn and wheat.

These carbohydrates are digested more slowly than their refined sugar counterparts, providing your body with essential vitamins, minerals and protective plant substances it requires.

They're also healthier because they won't cause abrupt insulin fluctuations that could harm its health.

Refined carbohydrates, on the other hand, are usually found in desserts, candies and snack foods and should be limited due to being high in kilojoules, saturated fat and added sugars and not providing many essential nutrients for our bodies.

However, if you are exercising or involved in high physical exertion refined carbs are a fast way to load your muscles and liver with glycogen and generally do not cause too much stomach discomfort.

Low Carbohydrate Diets

A low carbohydrate diet is an eating plan which restricts your consumption of carbohydrates, which may help you reduce weight and lower risk factors associated with heart disease and diabetes.

Before embarking on such a plan, however, it's wise to consult your physician or dietitian prior to undertaking it, particularly if you already have diabetes, are pregnant/breastfeeding, or are nursing.

Carbs can be found in foods like bread, pasta, potatoes, rice and corn; other sources include fruits, milk vegetables and legumes (beans).

A balanced and healthy eating pattern should consist of all these food sources.

Research suggests that cancer patients consuming a low carbohydrate diet may help improve outcomes.

Studies on animal models and humans with advanced or metastatic cancers have demonstrated this diet's beneficial properties by inhibiting tumor growth, prolonging survival, reducing chemotherapy toxicity while maintaining or increasing muscle mass mass, as well as providing some toxicity reduction benefits.

An effective approach to starting a low-carb diet is by eliminating added sugars, processed food and beverages such as soda.

Substituting these items for whole grains, non-starchy vegetables, dairy and protein from meat, fish and nuts and seeds; this may leave you feeling more energetic and satisfied.

Note that an overly restrictive low carbohydrate diet can result in vitamin and mineral deficiencies. Eating too few carbohydrates over an extended period can also put your body into ketosis, leading to headaches, nausea and bad breath. 

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Increased cortisol

Testosterone is an essential steroid hormone, playing an integral part in male sexual function, bone density, fat distribution and muscle strength.

Furthermore, testosterone regulates sperm production, metabolism and red blood cell formation; but as men age their levels tend to decrease.

Low-carbohydrate diets may have negative repercussions for their libido, performance and health.

A diet low in carbohydrates may increase stress hormone cortisol production which could potentially lower testosterone levels.

Studies conducted at the University of Worcester in England indicate that excessive protein consumption may also help lower testosterone levels.

A similar article published by Nutrition and Health journal on March 20,22 provided evidence to this effect.

This study included 27 intervention studies comparing low carbohydrate diets (LCD) to high-carbohydrate diets (HCD).

Researchers monitored resting total testosterone and cortisol levels as well as post-exercise testosterone and cortisol levels among participants.

Studies included in this research ranged in terms of specific objectives, but all included both a control group and low-carbohydrate diet (LCD).

Participants were randomly allocated either LCDs or HCDs and evaluated after three weeks.

Results revealed that LCDs resulted in moderate increases in resting cortisol, although these increases did not persist over long periods of time; they also led to greater post-exercise cortisol levels than traditional diets.

These findings support the hypothesis that lower carbohydrate consumption will increase insulin and leptin, leading to greater storage of fat and protein in skeletal muscles.

As a result, glycogen may become unavailable for exercise sessions in advance, prompting more use of energy-producing processes called gluconeogenesis as well as fat oxidation, possibly stimulated by cortisol.

Researchers also determined that LCD caused an increased increase in cortisol during intense aerobic exercise, especially at the start of each session, due to decreased glucose availability and faster drops in blood glucose following intense physical exertion.

After exercising, cortisol levels after peaking were associated with decreased erythrocyte counts suggesting immunosuppression; similar to findings that show how excessive protein intakes suppress immunity during physical exertion.

Points to note

This study included 27 year old men who were healthy, and followed either a low-carbohydrate or high-protein diet for three weeks.

Researchers then measured resting cortisol and testosterone levels; those on low-carbohydrate meal plans had significantly lower resting levels than those following high protein plans.

Although this study provides interesting findings, its limitations make it hard to draw any firm conclusions from it.

These include its small sample size and use of only one protein type; while variations in food used during trials could have had an effect on these findings.

Another limitation of the study is its comparison between two identical groups of participants, who may not represent the typical American diet or population as a whole.

Furthermore, researchers failed to control for variables that might influence results such as weight changes of more than 6.6 pounds or the use of hormones, medications, or phytoestrogens that might impact outcomes.

Decreased testosterone

Testosterone is an essential anabolic steroid in the human body, responsible for muscle growth and protein synthesis.

Many people don't realize that a low carbohydrate diet can significantly decrease a man's testosterone levels, negatively affecting his gym performance as well as his quality of life.

There are various treatment options for low testosterone such as hormone replacement therapy, diet modification and other supplements available - an appropriate balance is key for optimal health!

Whittaker and Harris conducted an in-depth analysis of 27 studies to understand how a low-carbohydrate, high-protein diet affects testosterone and cortisol, finding conflicting results among individual studies.

Their research indicated that moderate protein diets (less than 35%) with low carbs had no discernible impact on resting testosterone, while higher protein diets significantly decreased resting testosterone - likely due to breaking down protein for energy purposes in your body.

An inadequate amount of testosterone can cause loss of muscle mass, poor immune function, fatigue and low libido. Therefore, maintaining high levels of testosterone can improve athletic performance or enhance sexual performance.

One study examined seven individuals who followed a high-protein, low-carbohydrate diet for 10 days.

Their testosterone levels decreased and cortisol increased significantly - possibly because too much protein was broken down and released as ammonia into their systems.

Researchers believe that this change may have resulted from their bodies breaking down too much protein at once and producing too much ammonia as waste products.

Carbs are essential in producing testosterone and other anabolic hormones in our bodies, such as gonadotropin hormone release from testes neurons requiring steady blood glucose levels for proper function.

Thus, eating a balanced diet that includes carbohydrates, proteins and fats is of vital importance for optimal health.

Carbs have long been recognized to help increase sexual drive and build muscle mass.

Furthermore, carbohydrates can reduce inflammation while protecting liver damage caused by alcohol and junk food consumption.


In some cases, low-carbohydrate diets may actually help with testosterone and sexual function.

Researchers examined the effect of a low-carbohydrate diet on total testosterone and erectile function among hypogonadal men with metabolic syndrome.

They discovered that those eating a low-carbohydrate diet had higher total testosterone levels compared with moderate carb diet eaters, along with more physical activities to engage in which contribute to greater libido.

Furthermore, low-carbohydrate diets increased the number of men who were considered eugonadal (total serum testosterone > 300ng/dL).


If you're thinking about going low-carb, it is essential not to restrict all carbohydrates.

Instead, focus on eating whole foods while limiting refined carbs - for instance when making oatmeal for breakfast add some fruit or milk instead of sugar.

When cooking dinner use peanut or almond butter as a replacement for brown sugar - and include healthy fats such as avocado or salmon for extra nutrition!

One study examined how a high protein, low carbohydrate diet affects testosterone and cortisol levels among male exercisers.

Participants consumed either the high protein diet with reduced carbohydrates (or control diet) for three days prior to performing cycling tests on themselves.

The results demonstrated that after the low carbohydrate diet testosterone (and other anabolic hormones) declined while cortisol increased significantly.

However, according to researchers, any increase in resting cortisol due to short-term low carbohydrate diets could be due to temporary increases in gluconeogenesis caused by glucocorticoids.

Protein depresses the urea cycle and increases nitrogen excretion; hence more glucose is needed as energy. Furthermore, cortisol may rise because fatty acids cannot fuel brain functioning - leading to higher cortisol levels overall.

Researchers found that eating a diet high in proteins and low in carbohydrates led to an overall decrease in resting total testosterone and calculated free testosterone, despite having only conducted preliminary research with limited sample sizes.

As a result, more research must be conducted before drawing any firm conclusions regarding whether such eating patterns could indeed alleviate symptoms associated with hypogonadism in men diagnosed with metabolic syndrome.

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