Nutrition Myth #1 - Calories are Calories

25th June 2025

Calories are a measurement of stored energy, identified by the requirement needed to increase the temperature of 1 Ltr of water by 1°c.  I vividly remember burning a peanut in a Bunsen burner flame in school to see how much the temperature of the water above rose in a science lesson in school.  This usage of the calorie was adopted by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887, in an influential article on the energy content of food.

Unfortunately we don’t burn calories in our body by combustion.  Digesting a wooden log would not release the same energy as burning it.

One litre of petrol contains approximately 8,300 calories.   Drinking 330mls would not satisfy your daily caloric intake of 2,700 calories.  It would probably kill you.

And not all calories are equal.

Both carbohydrates and proteins contain around 4 calories per gram, where as fat contains around 9 calories per gram.   Our body utilises carbohydrates over protein preferentially as it is easier to metabolise.  Excess energy released from freely available carbs are stored as fat.  Hence, carbohydrate-rich diets are prone to weight gain - there is too much freely available energy which has to be stored.

Early research (1-3) on obese patients in the 1950’s, on calories restricted diets of 1000 calories per day showed significantly different weight losses as a consequence of being on 90% carbohydrate, 90% protein and 90% fat diets.

 

1000 cals at 90% fat diet = 408g weight loss per day

1000 cals at 90% protein diet = 272g weight loss per day

1000 cals at 90% carbohydrate diet = 108g weight gain per day.

 

Not all calories are equal.

Carbohydrates

Regardless of complexity – simple ‘white’ or complex ‘whole grain’ carbohydrates - are digested quicker than fats and proteins, which is the real issue.  Work by Qamar (4) examined gastric activity following ingestion of carbohydrates, fats and proteins after a period of fasting by measuring blood-flow in the mesenteric artery; the maximal responses were not significantly different but were reached at different times following ingestion: carbohydrate, 64% at 15 min; fat, 60% at 30 min; and protein, 57% at 45 min. 

Carbohydrates will be digested quicker than fats and proteins but in order to extract energy, fats and proteins will need to go through several additional chemical reactions, which carbohydrates do not. 

The Krebs Cycle is the process of creating Adenosine Triphosphate - the primary energy source for most cells.

During the process, one molecule of glucose is converted into two molecules of pyruvic acid, generating energy in the form of two net molecules of Adenosine Triphosphate (ATP).  Four molecules of ATP per glucose are actually produced, but two are consumed as part of the process.  

As energy is so easily obtain from carbs, it is your body’s preferred source of energy; once the glycogen stores have been depleted in the liver and muscles the body will then move onto burning fats before it attempts to breakdown muscles.

Conversely, because glucose is so easily obtained from carbs, any excess (your body only requires a certain amount of energy at any given point in time) is quickly and easily deposited as fat.

 

Fats

Where carbohydrates are quickly broken into glucose which can easily enter the Krebs Cycle, fats are the slowest digesting of the three macronutrients, but they are also the most efficient.  Every gram of dietary fat supplies the body with about 9 calories compared to 4 calories per gram of carbohydrate and protein.   Your body will preferentially utilise the glucose from carbohydrates as it is the most freely available to replenish the muscle glycogen stores.

Fats, on the other hand, require complex reactions to access the stored energy.

In the intestine, fats are broken down into fatty acids and glycerol.  These fatty acid chains are converted into energy via a process called beta-oxidation into Acetyl-CoA before they can enter the Krebs cycle along with oxygen to create ATP.

Energy and macronutrient needs must be met during times of high physical activity to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue.  Fat intake should be sufficient to provide the essential fatty acids and fat-soluble vitamins and to contribute energy for weight maintenance. (5)

 

Saturated vs Unsaturated Fats

Saturated fats are called "saturated" because of their chemical structure.  All fats are made up of carbon, hydrogen, and oxygen molecules.  Saturated fats are "saturated" with hydrogen atoms, which means they have the greatest number of hydrogen atoms possible and no double bonds in their chemical structure.  Like butter, they become solid at room temperature and are more likely to lead to health issues such as high cholesterol and heart disease.

Foods that contain saturated fats include:

·        Animal meat including beef, poultry, pork

·        Certain plant oils such as palm kernel or coconut oil

·        Dairy products including cheese, butter, and milk

·        Processed meats including salami, sausages, hot dogs, and bacon.

·        Pre-packaged snacks including crackers, chips, cookies, and pastries

 

Unsaturated fats are typically liquid at room temperature. They differ from saturated fats in that their chemical structure contains one or more double bonds.

They can be further categorized as:

Monounsaturated fats: This type of unsaturated fat contains only one double bond in its structure. Monounsaturated fats are typically liquid at room temperature and include canola oil and olive oil.

Polyunsaturated fats: This type of unsaturated fat contains two or more double bonds in its structure. They are also liquid at room temperature. Polyunsaturated fats include safflower oil, sunflower oil, and corn oil.

Examples of foods that contain unsaturated fats include:

·        Nuts

·        Plant oils

·        Certain fish like salmon, tuna, and anchovies, which contain omega-3 unsaturated fatty acids

·        Olives

·        Avocados

Some studies have shown that consuming a high amount of saturated fats may increase your low-density lipoprotein (LDL), also known as "bad" cholesterol.  High LDL levels may increase your risk of heart disease. (6)  However, there have been multiple studies that say saturated fat does not actually have a negative effect on your heart. (7)  Saturated fat increases the amount of large, buoyant LDL you have.  These larger LDL particles do not appear to increase your risk of heart disease.

On the other hand, small, dense LDL has been shown to contribute to atherosclerosis, the build-up of plaque on your arteries, which leads to heart disease.  Eating saturated fat doesn't appear to increase your small, dense LDL.  In a few cases, the risk of plaque build-up even went down when saturated fat was consumed. (8)

 

A greater issue is the type of fat source.  The type of saturated fat-containing foods you eat also seems to make a difference in your heart health.  One large study suggested that consuming dairy products may actually lower the risk of cardiovascular disease.  At the same time, including processed meats in your diet could increase your risk of cardiovascular disease. (9)  Not all fats are as dangerous as once thought. (10)

Overall, diets should provide moderate amounts of energy from fat (20% to 25% of energy); with the majority coming from unsaturated fats. However, there appears to be no health or performance benefit to consuming a diet containing less than 15% of energy from fat (5).

Fish, lean beef, olives, nuts and cheese all contain fats but, when eaten in moderation will have greater health benefits than chips, biscuits and processed meats.

 

Proteins

Protein is responsible for maintaining and growing muscle, and is key for recovery and sustaining a high-output lifestyle.

Protein can also be metabolized and used as an energy source for the body, but it’s not the preferred source of energy.

Proteins are broken down into individual amino acids; about 75% of which are used to synthesize new proteins which are used to build and repair tissues.  They're also used to produce enzymes that digest food and activate your metabolism. 

Only a small amount of carbohydrates (about 1,200-2,000 calories worth) can be stored in the liver and muscles as glycogen (11); in the absence of enough carbs, our body’s next preferred energy source is fats.

Under ordinary circumstances, our bodies only use protein for a small amount of daily energy -  around 5% of daily energy.  During strenuous activity, if glycogen stores are depleted, protein can provide up to 15% of energy (12).  As protein is not a quick or efficient source of fuel, and since it can’t be stored, any protein consumed that doesn’t get used immediately is converted into fat for storage. 

Protein is still key to maintaining a healthy energy level as it impacts the way we metabolize other nutrients.

References:

  1. Kekwick, A. & Pawan, G. L. S. (1953). Arch. Middlx Hosp. 3, 139.

  2. Kekwick, A. & Pawan, G. L. S. (1956). Lancet, 271, 155.

  3. Kekwick, A. & Pawan, G. L. S. (1957). Metabolism, 6, 447.

  4. Qamar MI, Read AE. (1988)  “Effects of ingestion of carbohydrate, fat, protein, and water on the mesenteric blood flow in man”.  Scandinavian Journal of Gastroenterol. Jan;23(1):26-30

  5. American College of Sports Medicine; American Dietetic Association; Dietitians of Canada. (2000) “Joint Position Statement: nutrition and athletic performance. American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada”. Medicine and Science in Sports and Exercise. Dec;32(12):2130-45

  6. Kim K, Ginsberg HN, Choi SH.   (2022)  “New, Novel Lipid-Lowering Agents for Reducing Cardiovascular Risk: Beyond Statins.”  Diabetes Metab J  Jul;46(4):517-532.

  7. Malhotra A, Redberg RF, Meier P.   (2017)  “Saturated fat does not clog the arteries: coronary heart disease is a chronic inflammatory condition, the risk of which can be effectively reduced from healthy lifestyle interventions.”  Br J Sports Med. 2017;51(15):1111-1112.

  8. Di Nicolantonio JJ, Lucan SC, O’Keefe JH.  (2016)  “The evidence for saturated fat and for sugar related to coronary heart disease.”  Progress in Cardiovascular Diseases. 2016;58(5):464-72.

  9. de Oliveira OMC, Mozaffarian D, Kromhout D, et al.  (2012)  “Dietary intake of saturated fat by food source and incident cardiovascular disease: The multi-ethnic study of atherosclerosis.”  American Journal of Clinical Nutrition.  96:397-404.

  10. Vafeiadou K, Weech M, Altowaijri H, et al.  (2015)  “Replacement of saturated with unsaturated fats had no impact on avscular function but beneficial effects on lipid biomarkers, e-selectin, and blood pressure: Results from the randomized controlled Dietary Intervention and VAScular Function (DIVAS) study.  American Journal of Clinical Nutrition. 2015;102(1):40-8

  11. American Dietetic Association, Dietitians of Canada, American College of Sports Medicine, et al. (2009) “American College of Sports Medicine position stand. Nutrition and athletic performance”. Medicine and Science in Sports and Exercise. Mar;41(3):709-731

  12. Eberle SG.  (2013)  “Endurance sports nutrition”.  Human Kinetics.