The Effect of the Glycaemic Index of the Diet on Energy intake and Testosterone

The Effect of the Glycaemic Index of the Diet on Energy intake and Testosterone

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


Carbs provide energy to our bodies in many forms. When broken down, glucose is released that is then utilized by cells as fuel to power our systems.

High glycemic index foods tend to digest quickly and raise blood sugar more rapidly than their low GI counterparts, according to the Glycemic Index ranking system which compares carb-containing food and beverages against pure glucose as their reference food source.

Glycaemic Index Explained

Carbs are essential sources of energy for your body, serving as one of three macronutrients that your body requires (protein and fat are the other two).

All carbohydrates are broken down into sugars in your digestive tract before being circulated through your bloodstream to provide energy to cells throughout your body.

Different food and drinks have different impacts on your blood sugar levels depending on how quickly they're digested and their rate of sugar production;

The Glycaemic Index (GI) provides an international system that ranks carb-containing products according to how quickly their contents raise blood sugar after consumption.

Its purpose is to rank carbohydrate-containing foods according to how quickly their sugars rise after ingestion.

Food's glycemic index (GI) score is determined by measuring how quickly its sugar enters your bloodstream following consumption and how high its blood glucose level remains afterwards, relative to pure glucose as a reference food.

The higher its GI rating is, the faster its sugars enter your system after eating; using this measurement helps individuals select foods which will be best for their needs.

Foods with a lower glycemic index rating tend to be healthier, as their sugars break down more gradually compared to those with a high GI and thus have less of an impact on blood sugar levels.

Examples of such foods (higher GI) are white bread, pastries and fried foods which cause spikes and dips in your blood sugar, leading to spikes and drops over time which could eventually lead to insulin resistance over time.

Glycemic load (GL), is another tool to help you assess how different foods might impact your blood sugar levels.

It accounts for how much of a particular food is likely to be eaten at one sitting and its effect on your blood sugar.

Calculated by multiplying its GI rating against its carb content per serving and then dividing by 100, an GL less than 10 is considered low; 11-19 makes moderate levels and anything over 20 is high.

The glycemic index value (GI/GI) of different foods can help you plan meals more effectively when trying to manage blood sugar levels.

However, it's important to keep in mind that many factors influence GI and GI/GI of food and beverages, including how they're prepared, the type of meal consumed and individual metabolic responses.

Carbohydrates Explained

Carbs provide energy quickly to our bodies, unlike fats or proteins. Carbs play an essential role in many foods and provide essential vitamins, minerals, fiber and more - though too many carbohydrates from processed food sources could lead to obesity and type 2 diabetes.

A healthY diet should include whole grains, beans and vegetables so we get all of our needed carbohydrates without overeating of sugars.

Carbohydrates are organic compounds composed of carbon, hydrogen and oxygen (CnH2O).

With its high water content, carbs are one of the most abundant and widespread organic substances - they're present everywhere from plants and animals to bacteria and algae cell walls.

All living organisms depend on carbohydrates as sources of energy.

Green plants produce glucose from carbon dioxide and water through photosynthesis.

Animals consume it to obtain energy for growth and vital functions. Higher organism cells use glucose to make fatty acids for long-term energy storage.

It serves as the preferred energy source for brain cells, and forms part of their nucleic acids which contain their genetic information.

Monosaccharides are the simplest type of carbs. These sugar molecules possessing an easy chemical structure are quickly broken down, leading to an immediate rise in blood glucose levels.

Glucose, fructose and galactose are three examples of monosaccharides; although all three share the same molecular formula C6H12O6. Their chemical structures contain different numbers of carbon atoms; thus classifying as isomers.

Complex carbohydrates consist of three or more sugar molecules linked together by complex chemical bonds.

Disaccharides include table sugar (sucrose), lactose from dairy milk and maltose while polysaccharides consist of long chains of monosaccharide units joined together.

These complex carbohydrates tend to be digested more slowly than simple ones and their impact on blood sugar is also gradual.

At digestion, complex carbohydrates are broken down into their simple constituents such as glucose through saccharification.

In humans and other animals alike, this process primarily takes place in the mouth and small intestine.

Salivary amylase plays an essential role here by breaking down disaccharides into their monosaccharide constituents while enzymes such as maltase, sucrase and glucosidase break down polysaccharides into glucose molecules in intestines.

Plants use polysaccharides to form their cell walls and protect themselves from being immersed into hypotonic solutions that would force water into their cells.

These same molecules make up starches as reserve energy stores in plants and glycogen as an energy source in animals.

Polysaccharides also play a structural role in algae and bacteria as well as constituting part of grasses and flowers cell walls as well as contributing majorly to wood, paper and other plant products.

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Effect of the Glycaemic Index of the Diet on Energy Intake

Glycaemic index and glycemic load of foods are measures of how quickly food is digested and absorbed into the blood stream.

High GI foods tend to be digested quickly and absorb glucose rapidly, leading to a rapid rise in blood sugar (hyperglycaemia), while lower GI foods digest slowly while still taking on glucose gradually, leading to more gradual rises (hypoglycaemia).

Food's GI/GL value can be determined by measuring incremental area under glucose curve following ingestion of test food relative to that following ingestion.

In one exploratory and short-term study, subjects were fed either a high GI diet or low GI diet ad libitum without altering their normal eating patterns or energy intake; total energy intake and percentage of calories from fat remained the same in both groups.

Low GI diets led to lower daily energy intake than high GI diets. However there was no difference in testosterone levels.

This is likely because their fat consumption levels were equivalent in both groups and that testosterone production can be affected by more than just total fat intake.

A decrease in glycaemic index could potentially improve insulin sensitivity while simultaneously decreasing levels and stimulating testosterone production.

Effect of the Glycaemic Index of the Diet on Testosterone

Testosterone, the steroid hormone, is essential to sexual function, bone mineral density and skeletal muscle mass.

Additionally, its presence acts as an important antioxidant; however, too high levels can reduce immune function, lead to oxidative stress and damage cells.

Hence why maintaining ideal testosterone levels with diet is so vital - specifically by cutting refined carbs and fat intake.

Diet can play a key role in helping maintain normal testosterone levels and benefit all parties involved.

Studies have demonstrated the correlation between meal composition and serum and salivary testosterone concentrations.

Particularly serum testosterone concentration, and diet type (low protein, low carb diet associated with increased serum and salivary testosterone concentrations; while in another diet consisting of equal amount of protein but higher carbs content resulted in decreased testosterone).

As is widely understood, diet can increase testosterone, with specific types of proteins having more of an impact than others. Diets rich in proteins like poultry, fish and dairy products seem particularly effective at increasing testosterone. Such foods should form the cornerstone of any healthy weight loss plan.

Diets rich in carbohydrates and sugary sweetened beverages were found to decrease both serum and salivary testosterone in this study, perhaps as glucose stimulated aromatase activity, thus decreasing testosterone production.

Testosterone levels can also be affected by other factors, including lipid and inflammatory status.

Adipose tissue inflammation as well as production of advanced glycosylation end products (AGEs) from Leydig cells has been implicated in functional hypogonadism associated with obesity.

Obesity's harmful effects on the endocrine system are thankfully reversible through lifestyle interventions.

Even modest weight reduction combined with a low carbohydrate, high protein diet results in increased testosterone and decreased cortisol levels.

These improvements in fat tissue, lipids, inflammatory markers and testosterone synthesis were accompanied by positive changes to body composition, muscular strength and bone density as measured by DXA. T

hough more research needs to be conducted in order to ascertain the long-term impacts of a carnivorous diet on testosterone and sperm health, such an approach may prove more successful at restoring normal testosterone levels than low calorie, starch based approaches.

Ketogenic diets may also be more beneficial to men's health than fad diets such as Atkins or South Beach diets which result in rapid weight loss but ultimately damage fertility and long term health.

Reports also indicate an increase in testosterone and improved sperm health, though further research needs to be completed in this area.

Effect of the Glycaemic Index of the Diet on Cortisol

Glycaemic index (GI) of food measures the impact that carb-rich food has on blood sugar levels after being eaten, using glucose as an example.

A food's GI value is determined by measuring how quickly its blood sugar spiked when exposed to small amounts of pure glucose; lower GI ratings correspond with lower rises.

100 is taken as the benchmark, so foods are ranked according to their GI ratings relative to glucose as their index value.

However GI doesn't take into account how much food is typically eaten at one meal so researchers developed another concept known as Glycemic Load (GL).

Here, food are ranked both by their GI value and then portion sizes used during one meal time.

Example: A medium-sized cantaloupe has an glycemic index (GI) score between 65 to 70.

One serving size would equal around one third of the whole fruit, so its GI rating exceeds that of sugar due to the greater likelihood of devouring an entire cantaloupe in one sitting than just one teaspoon of it.

12 female volunteers participated in this study by eating both a low GI diet and high GI diet for three days each, followed by a three day washout period between each diet.

Saliva samples were taken before and after each diet to test testosterone and cortisol levels in their saliva samples.

Testosterone and cortisol are secreted from adrenal glands at regular intervals throughout the day, peaking early morning hours.

Both hormones perform a range of functions including energy metabolism, stress responses and immunosuppression.

Cortisol being one of the key naturally-circulating GCs involved with many processes including metabolism, growth/reproduction/immune function.

The results of this exploratory short study indicate that decreasing both GI and GL diet levels has an effective way of increasing testosterone and cortisol production.

One reason this happens is due to improving insulin sensitivity and decreasing concentrations.

This allows the body to produce more testosterone after eating protein-rich meals while also aiding glucose management and maintaining normal glucose control.

As such, it is wise to divide proteins and carbohydrates between meals rather than eating large amounts all at once.

An individual should aim to consume approximately two parts carbohydrates for every one part protein at each meal.

Optimal ratios will differ based on the glycemic index (GI) rating of individual carbs.

By lowering its GI index rating, it is possible to optimize health in four or seven days by improving insulin sensitivity and decreasing levels, leading to an increase in testosterone production while decreasing cortisol.


A recent study suggests that altering your diet's glycemic index could alter salivary testosterone and cortisol levels.

The glycemic index ranks foods containing carbohydrates based on how they affect blood sugar levels after consumption; its purpose is to help individuals select healthier options like whole grains, fruit vegetables and beans with low GI numbers are seen as healthier options.

Lower Glycaemic Index scores mean foods have slower rates of raising blood sugar.

Although some low GI foods, like wholegrain foods, fruit, vegetables, beans and lentils can be healthy choices for you.

Using this single metric alone can be misleading; high Glycaemic Index foods, like watermelons or parsnips for instance can still be nutritious; chocolate cake has an inherently lower glycaemic Index value!

Plus foods containing fat or proteins reduce carb absorption to further lower its Glycaemic Index value!

Carbs that aren't immediately utilized as energy are stored as glycogen or converted to fat for future use, with one gram of glycogen providing approximately one day's worth of energy.

Some carbs may also be stored within muscle cells to serve as sources of fuel during intense exercise.


Testosterone, an important male hormone, regulates production of sperm, bone health and fat metabolism - while also playing an integral part in the development of male characteristics and behavior.

Low levels of testosterone have been linked to various diseases, such as diabetes. High blood glucose levels can damage arteries and lead to decreased testosterone production.

Excess body fat accumulation results in visceral fat build-up which reduces testosterone while increasing estradiol - creating a vicious cycle which decreases testosterone and heightens diabetes and cardiovascular risk factors.

A 2019 study revealed that following a low GI diet significantly reduced salivary cortisol and testosterone concentrations while simultaneously improving glycemic control in those living with type 2 diabetes and hypogonadism.

Testosterone therapy also positively impacted these variables with greater improvements seen among those adhering to their treatment (>75% adherence).

Together these findings suggest that diet modification combined with testosterone replacement may be able to alleviate diabetes symptoms as well as those caused by hypogonadism symptoms in individuals living with both conditions.

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