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Myth: A calorie is a calorie

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Myth: A calorie is a calorie

February 25, 2024, 2:22 PM IST 

The belief that all calories are equal is a widespread myth, even among the well-educated segments of our society. This notion is heavily promoted by the processed food industry to justify the increasing presence of ultra-processed foods in our diets. The argument posits that the source of calories—whether from protein, fat, carbohydrates, or whether the food is whole or refined, cooked or raw—is irrelevant. What matters, according to this myth, is the balance between calories consumed and expended, with any excess supposedly stored as fat in our bodies.

This perspective simplifies the issue to a matter of energy balance: consume more than you expend, and you’ll gain weight. Consequently, the narrative absolves processed foods of blame, placing the onus on individual discipline to “eat less and exercise more.” It reduces dietary advice to avoiding gluttony and laziness, suggesting that any calorie can fit into a balanced diet.

However, Dr. Robert Lustig from UCSF—one of the few remaining independent medical schools in the U.S.—has extensively researched this topic. He points out and I quote “This is the biggest lie in the history of medicine.” The food industry’s vested interest in perpetuating this myth has misled many into believing it’s an incontrovertible truth. For instance, the sugar industry once advertised that three teaspoons of sugar were less fattening than an apple, diverting criticism from sugar to other foods.

The Fallacy of Portion Control

The “A Calorie is a Calorie” mantra suggests that a daily deficit of 500 calories should lead to losing one pound per week. However, many people find their weight loss stalls after initial success, leading to frustration. This phenomenon occurs because the human body, intelligent and adaptable, reduces its metabolic rate when it senses a food shortage—a survival mechanism honed over millennia. Our basal metabolic rate can drop, conserving energy during periods of scarcity, similar to how some animals hibernate.

Not All Consumed Food is Absorbed

The first thing to understand is that it is not the calories consumed that matter, it is the calories absorbed that matter. How many calories get absorbed in the body is a function of many factors. Firstly the speed at which the digested food travels through the small intestine and secondly the absorption rate while this food is traveling through the small intestine. Both of these are a function of fiber content of the food. Plant based whole food (PBWF) is full of fiber and as a result it has high motility and travels through the small intestine, where most of the absorption takes place, quite fast. PBWF also has nutrients embedded inside fibers that take time to be extracted. As a result the PBWF gets absorbed only partially and the balance reaches the colon where it feeds the microbes which in turn make essential nutrients for the body. A good example of this is resistant starch present in beans.  When beans are consumed, a significant portion of calories don’t get absorbed in small intestines (hence the title resistant) and move on to colon where our microbes feed on them.  This is also called the second meal effect.

Another good example is that of almonds. There are 165 calories in an ounce of almonds but when we eat them, only 135 get absorbed. Where do the other 30 calories go? The fiber in the almonds

Is both soluble and insoluble. The insoluble fiber forms a mesh like a fishnet and soluble fiber forms a gel which is filling the wholes in the net. Together they create a barrier in the upper part of small intestine which restricts the absorption of starch and glucose into liver. The liver therefore does not get overloaded and new fat is not formed from the fructose which in the absence of fiber does get formed in a process  called de novo lipogenesis (DNL)

DNL is a complex and highly regulated process in which carbohydrates from circulation are converted into fatty acids that are then used for synthesizing either triglycerides or other lipid molecules. DNL helps keep the sugar and insulin levels down. High insulin level is very harmful as it drives abnormal growth. It drives vascular muscle growth that leads to coronary artery disease. It also causes prostate growth. The 30 calories that did not get absorbed go to the colon where our microbes feed on them.

As you can see from two examples above, the calories eaten are not necessarily calories absorbed. This explains why a calorie is not a calorie.

Food Processing and Its Impact

The way food is processed before consumption also affects its health impact. The same 100 calories from sugarcane can vary greatly in their effect on health depending on whether they’re consumed as fruit, juice, jaggery, or white sugar.

PBWF vs. Refined Food

Refined foods are devoid of fiber as a result they (1) move slower through small intestines taking longer to reach colon and (2) they get absorbed readily as the intestines don’t have to work as hard to extract nutrients from the mesh of fibers. This dual effect makes most of the calories get absorbed in small intestines only, leaving nothing or little for the microbes waiting in the colon. The microbes in colon, when regularly deprived of fibers and starch, start to feed on mucosal layers creating a breach exposing intact protein in food to colon lining made of tight junction epithelial cells. A leak through this layer causes various auto immune diseases.

Circadian Rhythm

The timing of calorie consumption  also matters due to our body’s circadian rhythms, affecting how food is processed at different times of the day. Recent (2017) Nobel Prize-winning research has shed light on these mechanisms, highlighting the importance of synchronizing. Dr. Satchin Panda’s research at the Salk Institute in SanDiego has shown that carbohydrates consumed during daytime are handled differently than during night. During daytime they are kept as readily available glucose in the blood and during night they are quickly converted into triglycerides and stored away as fat.

Macronutrient as a Sources of Calories

The source of calories—whether from proteins, fats, or carbohydrates—significantly influences health outcomes. Calories from proteins, for example, affect the body differently than those from fats or carbohydrates. Even within a single macronutrient category like carbohydrates, the impact varies based on the type, such as starch, glucose, or fructose.

Calories From Carbohydrates 

Carbohydrates, which include starches, glucose, and fructose, are metabolized differently in the liver. Starches are converted into glucose by the liver and distributed throughout the body. Table sugar, comprises equally of glucose and fructose and they are processed differently by the liver. Glucose circulates in the blood, while fructose can be converted into glucose for energy or into fat for storage, depending on need which is judged by insulin levels. High insulin levels signifies the sufficiency of glucose in the blood and prompts the liver to convert fructose into fat, which can be stored in subcutaneous fat cells or, if the process is overwhelmed, lead to ectopic fat deposits. This can contribute to conditions like non-alcoholic fatty liver disease (NAFLD), visceral fat accumulation, and insulin resistance, the main cause of type 2 diabetes.

So once again you can see that a calorie is not a calorie. Glucose calorie is kept as readily usable glucose but fructose calorie may be stored as fat.

Calories from  Protein 

Human body is very efficient in recycling protein as a result the protein requirement by the body is rather minimal. So liver converts all extra protein into fat or carbohydrates by a process called deamination. Deamination is the opposite of amination and it is a type of post-translational modification (PTM) in which an amine group is removed from a protein. This process creates organic acids which provide energy (ATP) to cells.

This process costs energy, in fact twice as much energy as what it takes to burn carbohydrates. So the net result is that protein provides less calories than carbohydrates, by some estimates as much as 30% less. This explains the popularity of keto diets but this extra burden on liver and kidneys leads to problems in those organs as we age.

Calories from Fat

All fats are 9 calories per gram but it is wrong to think that all fats are equal. Omega-3 fats are very healthy fats but trans-fats are very unhealthy. Trans-fats cannot be broken down by our body cells into energy (ATP).

When we run out of glucose stored in the liver and muscles as glycogen, the body can use fat to provide energy. Theoretically it is correct however in practice the body first sends hunger pangs as a signal to consume more sugar or starch (which provide glucose more readily) before digging into it’s reservoir of fat which is kept for rainy day when food may not be available. So this is another reason a calorie is not a calorie.

Myth: Exercising Alone Will Take Care of My Health

One common myth many young people, who exercise regularly, have is that “Nothing wrong can happen to them because they physically work out regularly”. As a result they become lax in dietary discipline. The data shows that about half of the people, who die after their first heart attack, have no signs of cardiovascular disease. Dr. Robert Lustig of UCSF points this out clearly in his book Metabolical suggesting that of the 8 mechanisms for a healthy body, exercise helps only 4. Food is most important for good health and must not be neglected.


As you can see from explanations given above, it is not only what food you eat that matters, it is also what is done to the food and what your body’s metabolic response is to the food that matters. This underscores the principle that not all calories are equivalent, highlighting the importance of considering the source and type of macronutrients in dietary choices.

To Read this article on Times of India click here

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