Health effects of the calorie counting diet

For many years the well-known diet that relies on counting and restricting calories in meals was deemed to be the best way to lose weight and reduce the fat stored in your body.  The calory counting diet was based on earlier research, which indicated that when individuals consume more calories than their bodies use for energy, the excess energy is primarily stored as fat tissue. 

This simplistic “calories in, calories out” model implies that weight loss is as straightforward as burning more calories than what you consume.  This assumes that caloric intake and expenditure are accurately measurable and related to weight loss. 

This model’s major limitation is that not all calories affect the body equally.  Recently published studies proposed a “carbohydrate-insulin model”, with a different causative pathway for weight management.  This model suggests that it is not only calorie quantity, but more so the type of calorie that plays a crucial role in weight gain.  For example, 500 calories from whole-grain rice with a low glycemic index, which is digested slowly, affects the body’s metabolism vastly different than 500 calories of refined white sugar with a high glycemic index, which causes a rapid spike in blood glucose levels.

Another limitation of the “calories in, calories out” model is that it excludes factors such as genetic predisposition, body type, insulin sensitivity, and hormonal profile, which all create unique ways in which the individual person’s body may be susceptible to weight gain.

Key differences between these two weight loss models:

A review of the metabolic and hormonal mechanisms that drive variability in weight management outcomes of individuals was published December 2024 in the International Journal of Molecular Sciences.  This review compared the key features of the “calories in, calories out” model with the “carbohydrate-insulin” model:

Feature	“Calories In, Calories Out”	Carbohydrate–Insulin Model
Core Concept	Weight change is governed by energy balance, where weight loss occurs by burning more calories than consumed.	Emphasizes calorie quality over quantity, suggesting that carbohydrate intake influences insulin response and fat storage.
Primary Focus	Energy balance (calories consumed versus calories burned).	Impact of carbohydrate types on insulin and subsequent fat storage.
Mechanism of Weight Gain	Excess caloric intake relative to expenditure results in weight gain.	High carbohydrate intake, especially high-glycemic-index carbohydrates, elevates insulin, promoting fat storage.
Role of Macronutrients	All macronutrients contribute equally to total caloric intake; their effect on metabolism is not emphasized.	Carbohydrates, particularly refined ones, impact insulin levels, thereby affecting metabolic and hormonal responses.
Hunger and Satiety Regulation	Hunger is a byproduct of caloric deficit; it does not fully account for hormonal influences on appetite.	Insulin response from high carbohydrate intake can create cycles of hunger and satiety, potentially leading to overeating.
Impact on Fat Storage	Fat storage is viewed as a result of caloric surplus.	Insulin promotes fat storage, particularly after high-carbohydrate meals.
Effectiveness of Low-Carb Diets	Not specifically emphasized; all caloric deficits can theoretically induce weight loss.	Low-carb diets reduce insulin levels, potentially reducing fat storage and increasing fat mobilization.
Metabolic Adaptations	Assumes a direct, linear relationship between caloric intake, expenditure, and weight change.	Recognizes adaptive mechanisms where high insulin levels can limit fat mobilization, influencing weight plateau or gain.
Application in Diet Planning	Caloric tracking and balance are prioritized; diet quality is less emphasized.	Focuses on carbohydrate quality and glycemic index to modulate insulin and manage body fat.
Limitations	Simplistic; may overlook inaccuracies in food labels, metabolic adaptations, and hormonal influences.	May not fully explain weight loss variability across individuals; less focus on caloric balance in overall diet.

The role that body types play in weight management:

The terms ectomorph, mesomorph, and endomorph refer to three classical body types (somatotypes). People are rarely one pure type, but these categories generally describe how easily you build muscle, store fat, and maintain your weight. 

Ectomorph:

• Characteristics: Naturally thin and lean with small joints, narrow hips, and long limbs.
• Metabolism: Fast; they often burn calories quickly and struggle to gain weight or build muscle mass.
• Fitness & Diet: May need a higher-calorie, protein-dense diet combined with heavy resistance training to help preserve lean muscle during weight loss, as well as to build and maintain muscle.    

Mesomorph:

• Characteristics: Naturally athletic and muscular build.  Generally, has a higher muscle mass.
• Metabolism: Efficient; they lose and gain weight easily.
• Fitness & Diet: Genetically predisposed to build muscle quickly. They tend to respond well to a balanced diet and regular, varied workouts. 

Endomorph:

• Characteristics: Softer, curvier, or stockier structures. They typically have a medium-to-large bone structure and often carry excess weight in the lower abdomen, hips, and thighs.
• Metabolism: Slower; they have a higher tendency to store body fat.
• Fitness & Diet: Tend to lose weight more slowly. They often benefit from a focus on lean proteins, moderate carbohydrate control (as they may be prone to insulin resistance), and consistent resistance and cardio training.

Some other individual differences also impact weight management:

Metabolic rate: Metabolic rate is the amount of energy your body expends in a given period, measured in calories or joules.   Understanding your metabolic rate helps with weight management, as it is an indication of the rate at which you burn calories.

Resting Metabolic Rate (RMR) refers to the total number of calories your body burns while completely at rest, as if you stayed in bed all day.  

Basal Metabolic Rate (BMR) is the number of calories you burn as your body performs basic (basal) life-sustaining functions, including the energy your body uses to maintain basic functions such as the heartbeat, cell production, respiration, maintenance of body temperature, blood circulation, and nutrient processing.

Your unique metabolic rate is influenced by a number of factors, including age, weight, height, gender, environmental temperature, dieting, and exercise habits.

Having a balanced, healthy metabolism is better than having an extremely fast or slow one. While a fast metabolism burns calories quickly, making it easier to stay lean, a slow metabolism is efficient at storing energy, but makes weight loss harder

Hormonal control of metabolism: The body’s metabolism of the three macronutrients, namely carbohydrates, fats, and proteins, is orchestrated through complex metabolic and hormonal networks in the body. These chemical messengers regulate nearly all bodily functions.  Hormonal signals integrate with metabolic pathways to promote or inhibit energy storage and expenditure across different tissues, creating a finely tuned balance in response to dietary intake.  

This integration can be illustrated by using insulin as an example, as it is often called the “king metabolic” hormone.  Insulin lowers blood glucose levels by allowing cells glucose uptake from the blood stream.  Insulin also affects the metabolism of carbohydrates, fats, and proteins. 

• Insulin’s effect on carbohydrates:  Insulin turns on a process called glycolysis, which breaks down glucose to create energy for the body.  Insulin also turns on glycogenesis, which is the process that stores extra glucose in the liver and muscles as a backup fuel called glycogen.  When glycogen stores are full, insulin convers extra glucose into fat (lipogenesis) for long-term storage.
• Insulin’s effect on fats: Insulin promotes fat storage and stops fat breakdown. When insulin levels are high, the body stores excess energy from food as fat.   As long as insulin is active, the body uses glucose for energy and keeps stored fat locked away.  Insulin resistance means your cells stop responding well to insulin’s signal – in response the pancreas then makes more insulin to try to force glucose into your cells.  High levels of insulin keep your body in a constant state of fat storage, which makes it hard to lose weight. 
• Insulin’s effect on proteins: Insulin is a vital hormone for building and saving proteins in the body. It works by moving amino acids (the building blocks of proteins) into cells, which then build new proteins and stops the body from breaking down existing proteins.  Insulin does this by activating the mTOR pathway in cells, which tells the body to use amino acids to create new proteins. This helps your body grow and repair tissues.  Insulin also acts as an anticatabolic hormone, as it stops muscle tissue from breaking down and protects existing muscle mass. 

Insulin is only one example of how hormones affect an individual’s metabolism, which is further influenced by individual differences in hormone expression.

Calorie restriction triggers certain adaptive mechanisms in the body:

Counting calories inevitably means restricting calorie intake for the purpose of weight management.  Calorie restriction triggers a number of adaptive mechanisms, which the body would normally use as survival mechanisms to prolong energy reserves when food is scarce.  The intensity of these adaptive mechanisms would differ between individuals.

• Adaptive thermogenesis: Thermogenesis is literally defined as heat production in the body and refers to the process by which the human body produces heat to maintain a stable core temperature, usually around 37° C.  It is driven by metabolism, which is the burning of calories to keep the body functioning.  The body generates heat in three main ways, firstly the energy used for vital organ functions, cell repair, and breathing, all of which naturally releases heat as a byproduct.  Secondly, heat is produced by the energy required to chew, digest, and store the nutrients from the food you eat.  Thirdly, physical activity where any movement creates heat in the muscles. Calorie restriction lowers thermogenesis and reduce Basal Metabolic Rate (BMR) to conserve energy.  Adaptive thermogenesis occurs as a survival mechanism, helping the body endure when food is scarce. 
• Appetite stimulation: During calorie restriction, the hormonal signals that drive appetite regulation starts to intensify the body’s urge to seek food and restore energy reserves.  A number of mechanisms is involved.  Ghrelin (known as the “hunger” hormone) levels rise and stimulate appetite, while also sensitizing dopaminergic reward pathways in the brain to enhance the appeal of high-calorie foods.  Reduced insulin levels due to calorie restriction lower satiety effects, which is further aided by decreased glucagon-like peptide-1 (GLP-1) levels that also weakens satiety signals.  These adjustments heighten hunger and lower the body’s ability to suppress calorie intake. 
• Ketogenesis: With reduced caloric intake, the body shifts from burning carbohydrates to using fat as a primary energy source.  When the body lacks carbohydrates, it initiates a process called ketogenesis, whereby the liver converts stored fat into energy molecules called ketones, The liver releases these ketones into the bloodstream as a source of energy for the cells in the body. 
• Muscle protein degradation: Caloric restriction also triggers muscle catabolism, a process by which the body breaks down its own muscle tissue to use for energy, leading to the loss of muscle mass and strength.  Muscle catabolism also supplies amino acids for gluconeogenesis, the process in which the liver makes new glucose from non-carbohydrate sources such as fats and proteins. This ensures a steady glucose supply for glucose-dependent tissues such as the brain and red blood cells.  Cortisol rises in response to caloric restriction, promoting proteolysis in skeletal muscle.  Proteolysis is the breakdown of proteins into smaller peptides or amino acids.  Cortisol activates proteolytic enzymes to supply amino acids for gluconeogenesis, the process by which the body makes glucose from non-glucose sources. The brain and red blood cells need glucose for energy.  Growth hormone (GH) levels may increase with caloric restriction, stimulating lipolysis, the process of breaking down stored fat molecules into glycerol and fatty acids which the body use for energy, reducing muscle protein breakdown.  Interestingly, fluctuations in testosterone and estrogen can also influence muscle preservation. Testosterone plays a role in reducing protein breakdown, while estrogen modulates muscle sensitivity to insulin, indirectly preserving muscle tissue.

Variation in individual responses to diet.

Individual responses to diet differ amongst individuals, whether in terms of fat gain, muscle gain, fat loss, or muscle preservation.  These variations arise from a strong interplay of genetic predispositions, epigenetic modifications, behavioural influences, and environmental factors. Together, these factors contribute to an individualised metabolic response, which provides some insight into why individuals experience unique outcomes in response to similar caloric conditions.

In addition, not all calories are created equal, says Harvard.  Apart from the major role that metabolism play, there are two other main factors that affect the way the body processes calories.

The gut microbiome: There are trillions of organisms living in the gut, and the predominant types may influence how many calories your body absorbs from food. Researchers have found that people who are naturally thin have different types of organisms living inside them than those who are overweight. This may occur because some types of bacteria in the gut are able to break down and use more calories from certain foods than other types of organisms.  As the gut microbiome is influenced by dietary patterns and lifestyle, it significantly contributes to individual variability in weight gain.   For example, diets rich in processed carbohydrates and saturated fats promote a microbiome composition that enhances energy harvesting, predisposing some individuals to greater fat accumulation. On the other hand, a fiber-rich diet supports a more favorable microbiome that increases satiety, and may limit fat gain during overfeeding.  The interplay between diet, microbiome, and host metabolism plays a crucial role in individual differences in weight management.

The type of food you eat: Your food choices may also influence your calorie intake, and not just because of their specific calorie content. A landmark 2019 National Institutes of Health (USA) study published in Cell Metabolism found that eating processed foods seems to spur people to eat more calories compared with eating unprocessed foods. Participants were split into two groups and were offered meals with the same number of calories, as well as similar amounts of sugar, sodium, fat, fiber, and micronutrients. But there was one key difference: one group was given unprocessed foods, and the other got ultra-processed options. After two weeks, the groups switched and ate the other type of diet for the following two weeks.  People who ate the ultra-processed food gained weight and ate 500 calories more each day on average. The same people’s calorie intake decreased when they ate the unprocessed foods. 

Successful weight management:

According to Harvard, counting calories is not a dependable way to manage your weight.  

Successful weight management focus on diet quality, which means cutting down or eliminating processed foods and instead focussing on unprocessed foods, including lean meats, whole grains, and abundant fruit and vegetables.

Regular exercise of at least 150 minutes of moderate intensity exercises is required each week.  Moderate intensity exercise is like walking up a hill, at a level where you can still talk, but not sing.

Poor sleep quality can lead to weight gain, as well as a sleep schedule that is out of sync with the body’s natural daily pattern, known as circadian rhythm.  A lack of sleep affects your weight in much the same way as hormonal shifts, making you want to eat more.

Stress, like poor sleep, can lead to weight gain. Managing stress levels can help you keep excess weight at bay.

Conclusion:

The “calories in, calories out” formula for weight loss has lately been viewed as a myth, as it oversimplifies the complex process of energy intake and expenditure in the body.  In addition, it fails to consider the mechanisms that our bodies trigger to counteract a reduction in energy intake.  One may achieve short-term weight loss but are more than likely to regain it later.

What’s more, calorie counting takes the pleasure out of eating!

References:

Beyond calories: Individual metabolic and hormonal adaptations driving variability in weight management – a state-of-the-art narrative review.  Published December 2024 in International Journal of Molecular Sciences.  25(4).  PubMed Central.  National Centre for Biotechnology Information.  US National Library for Medicine. National Institutes of Health.  USA.  (www.ncbi.nlm.nih.gov)

Stop counting calories. Put the focus on food quality and healthy lifestyle practices to attain a healthy weight.  Published 1 October 2020.  Harvard Health Publishing.    Harvard Medical School.  (www.health.harvard.edu)

It’s time to bust the ‘calories in, calories out’ weight‑loss myth.  Published 5 June 2023.  The Conversation.  (www.theconversation.com)  (The Conversation is funded by the National Research Foundation; eight universities, including the Cape Peninsula University of Technology, Rhodes University, Stellenbosch University and the Universities of Cape Town, Johannesburg, Kwa-Zulu Natal, Pretoria, and South Africa.  It is hosted by the Universities of the Witwatersrand and Western Cape, the African Population and Health Research Centre and the Nigerian Academy of Science. The Bill & Melinda Gates Foundation is a Strategic Partner.) 

Why calorie counting doesn’t always work.  Published 19 July 2023.  Nutritionist Resource.  UK.  (www.nutritionist-resource.org.uk)

Epigenetics, health, and disease.  Published 31 January 2025.  U.S. Centers for Disease Control and Prevention.  (www.cdc.gov)

Mechanisms of nutritional and hormonal regulation of lipogenesis.  Published April 2001 in EMBO Reports.  PubMed Central.  National Centre for Biotechnology Information.  US National Library for Medicine. National Institutes of Health.  USA.  (www.ncbi.nlm.nih.gov)

Understanding metabolic adaptation and weight loss.  Published online 4 April 2023.  SIGNOS.  (Continuous glucose monitor manufacturer.)  (www.signos.com)

Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of Ad Libitum food intake.  Published May 2019 in the journal Cell Metabolism.  (www.cell.com)

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