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All calories are not created equal

MUSC News Center | January 22, 2015

Fruit and Veggies
Sarah Pack
Are all calories the same? 

Weight Loss. It’s a popular topic every January yet even the most educated health professionals quibble over the best approach to achieve it. One popular debate revolves around the calorie – the unit of measure for energy:  The question is, are all calories the same? Can weight loss can best be achieved by consuming less of them, or does the source of the calories matter as much, if not more, than the total calorie count? And just where does that fat go when you lose it, anyway?

Whether you are a believer of the “a calorie is a calorie” philosophy or the “calorie sources” argument, researchers can agree on the following weight loss facts:

  • To lose body fat, the body needs to use more energy than it consumes to kick off the breakdown of fat (or the metabolism of the triglycerides stored in adipose tissue).
  • The body uses energy for essential functions like breathing; thermogenesis, which is the metabolism of your food; and purposeful movement like walking - the latter being the area individuals can most directly influence by moving more.
  • There is no agreed upon method that constitutes the best way to reduce caloric intake. Whether counting calories or considering the calorie source, experts agree that minimally processed, high fiber foods; most vegetables; beans; lean meats; and unsweetened tea or coffee should be encouraged. Conversely, highly processed items; sugary beverages like sweetened tea and full-sugar soda; baked sweets; candy; fried foods; and snack chip items should be discouraged.

For an interesting illustration, see this site.


How do I kick off the breakdown of fat?

The key is to losing weight is to create a need for the body to use the stored energy reserves from fat. Since the body requires energy 24/7, there is always some energy source available in the blood for metabolism. When the body’s energy needs exceed the amount of energy available, there is a demand to release the energy stored in fat cells. Triglycerides – the body’s storage form of fat - are metabolized and the end products, carbon dioxide and water, are excreted from the body. The side effect of this is a loss of body mass.

In attempts to lose weight, individuals often strive to induce this energy imbalance by restricting energy intake, like eating less, and/or increasing the body’s energy needs by moving more. The challenge, as anyone who has tried to lose weight can tell you, is that energy intake and energy expenditure are biologically linked. When energy is restricted and those blood levels of energy sources fall, the body tries reset the balance by making you feel hungry so you search for food and/or feel more tired so you move less.

How do I create energy imbalance?

One approach to creating energy imbalance is to eat a diet lower in calories than the body uses on a daily basis for essential functions, thermogenesis and movement. Dieters are often taught to focus on replacing high calorie foods with low calorie foods, regardless of the source of calories, to create this deficit: bottom-line, find some extra calories and cut them out!

This calorie counting philosophy does have its critics. The source of the calories, these critics argue, enter into the metabolic pathway in different ways, each uniquely triggering a hormonal pathway that influences appetite, satiety, energy storage or energy utilization. The most antagonizing example is concentrated sources of rapidly absorbable carbohydrates. Simple carbohydrates and refined sugars cause a rapid increase in blood glucose levels and a corresponding surge in insulin levels which drive ingested nutrients into cells for storage. This lowers the levels of available energy in the blood causing the biological response: hunger.

Many experts refer to the second law of thermodynamics to further support the “calorie sources” theory. This law states that no system is perfectly efficient and some energy will be lost or unrecoverable. In reference to weight loss, this inefficiency is desirable. This principal can be applied to thermogenesis, or energy lost during the metabolism of the foods we eat. On average, lipids lose 2 percent of their energy when they are metabolized – a relatively efficient process. Carbs lose about 7 percent and proteins lose 25-30 percent. Proponents of the thermodynamic argument have illustrated that as carb intake decreases and protein intake increases, more calories are ‘lost’ to thermogenesis, a desirable side effect for the dieter.

Screen grab from Ruben Merrman's video "Where does fat go?" 

To learn how the first law of thermodynamics, which states matter cannot be created nor destroyed, dictates where pounds go once they are lost, watch Ruben Merrman’s video “Where does fat go?”

What will work for me?

While the academics continue to investigate the nuances of metabolism, remember that what works for one individual will be different from what works for others. For all of us, the key to losing fat is to take in fewer calories than our bodies use, but certain foods may help you reach that goal more quickly and without the side effects of feeling hungry and tired. In my opinion, the foods that do this are things that are considered perishable and should meet at least one of these criteria: it needs to be refrigerated, washed, peeled or trimmed, cooked and/or seasoned. If you could stick it in the cabinet and it would still be ‘fresh’ come Easter, it’s not a good choice.

Debbie Petitpain, RDN, is a Sodexo Wellness dietitian in MUSC’s Office of Health Promotion.




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Resources >>

MUSC Weight Management Center

MUSC Office of Health Promotion

MUSC Wellness Center

MUSC News Center archives


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