Are All Calories Created Equal in Weight Loss?

  

Key Points

• The law of thermodynamics suggests that energy must be conserved, but this may be an oversimplification of the weight management challenge.
• Certain nutrients may have a more potent satiating influence than others, which may help people manage their intake and weight.
• Understanding these influences may help fitness professionals support their clients with weight loss and weight loss maintenance goals.

Energy in versus energy out: The end of the story?

The weight loss debate centers often around the validity of the law of thermodynamics. This law of physics, when applied to human physiology and energy metabolism, suggests that if we eat food containing energy (measured in kilocalories) than we must either expend this energy or convert it and store it as fat. By extension, many weight loss paradigms maintain that whether you eat a handful of jelly beans or a baked potato (about the same amount of energy), and this intake represents a Kcalorie surplus, both will be stored as fat with equal efficiency.

Energy balance refers to someone eating what they expend. So, if all of the foods, drinks, and supplemental nutrition are equal to everything they “burn” (basal metabolic rate, + daily activity + exercise activity) then they are said to be in “energy balance.” There is no doubt that people gain weight when there is an energy imbalance, in other words, when they eat more than they expend. How much they gain depends on the magnitude of difference between energy in and energy out, and how long this imbalance occurs. The rate of gain can even be predicted if the magnitude of difference and duration are known. However, the term “energy balance” is somewhat of a misnomer, because we are never really in complete energy balance. It is the corrective responses (eating a little more one day and a little less on another) that result in weight regulation. People who eat a little more one day and a little less the next, without even thinking about it, have what scientists consider a “healthy corrective response” and they can maintain their weight without a lot of conscious manipulation (i.e. dieting, calorie counting etc.) However people with less vigorous corrective responses experience a slow upward drift and weight is gained gradually (1). 

If we presuppose that people are like math problems (Calories in versus Calories out), the solution to weight gain seems simple, eat less and move more. But if Calories are the beginning and the end of the story, why do we engage in endless debates about demonic nutrient categories, food timing, and the delivery of magical combinations of nutrients for weight loss? If 200 calories of carbohydrate equals 200 calories of protein, then why do we debate high protein versus low fat diets? Because scientists are actively examining why this deregulation of calories occurs in some people and not others, and this discussion gets attention at the consumer level. Unfortunately here, mythology and marketing often prevail over evidence, hence the $19.6 billion spent in the United States on sports and weight loss supplements alone (2).

It’s not which diet, but how closely it’s followed that matters!

There have been a number of studies using foods that were tagged with nonradioactive isotope (carbon-13) that show the better adherence to a diet, the greater the weight loss. In other words, it is adherence to a diet, and not the diets themselves that makes a difference (3). Evidence shows that any diet will result in weight loss if it reduces calories that were previously over-consumed.

Therefore, if the type of diet people consume matters less than their ability to follow it, helping weight loss clients adhere to their program becomes even more important. Additionally, while energy balance is vital to weight loss, nutrition scientists and counselors are also interested in the quality, not just quantity, of Kcalorie intake. Nutrient density – the amount of essential nutrients per Kcalorie -- is a critical concept for healthy eating in general, and it becomes even more important when restricted budgets for weight loss are implemented. Like a financial budget, when funds are limited, the fundamentals must be covered before any “extras” can be accommodated. If all of a sudden you have a drop in income, you are going to make sure that you’re essentials (rent, car payment, health insurance, etc.) are covered, before non-necessities are purchased. Likewise, with a restricted food budget, the essential nutrients (vitamins, minerals, fiber and phytochemicals, as well as necessary carbohydrates, fats, and proteins) must be provided before the energy budget can accommodate discretionary Kcalories. 

In an attempt to better understand which programs demonstrate the best compliance, scientists explore the advantages of macronutrient manipulation. Many studies concur that the use of a higher-protein diet may improve perceptions of satiety during energy restriction, which may facilitate a reduction in energy consumption under free choice dietary conditions. Controlled energy intake in association with a moderately elevated protein intake may also help dieters maintain or accrue fat-free mass (4, 5).

Also being researched in the context of improved satiety are foods with a low glycemic index (GI) and their contribution to an energy restricted program. The glycemic index, first reported on in the 1980s, is a ranking of a food’s ability to contribute glucose to the blood stream. It is a measure of blood glucose excursion per unit of carbohydrate. Foods with a high GI are rapidly digested, absorbed, and transformed into glucose. These processes cause accelerated and transient surges in blood glucose and insulin, and possibly an earlier return of hunger sensation and consequent excessive caloric intake. Some studies (glucostatic theory), suggest that differences in insulin response between low GI meals (or meal replacements) and high GI meals may be responsible for prolonged satiety and this may prove an effective method for reducing caloric intake and achieving long-term weight control (6). 

What can fitness pros do to help?

Although any dietary or lifestyle program must be personalized, it might be useful for fitness professionals to suggest some of these strategies to help their clients feel fuller and eat less. For example, recommending higher fiber, minimally processed foods will not only increase health promoting nutrients, but may also help clients feel fuller, longer because they are lower GI foods. Suggesting that a client include a few ounces of protein (string cheese log, nuts, tofu, chicken, etc.) may also help them stay fuller throughout the day and reduce some of the hunger driven snacking. While none of these areas of exploration (low GI, higher protein, etc.) should become the exclusive principle around which a dietary program is developed, incorporating some of them into your existing nutrition guidance portfolio may help some people eat less. 

In summary, while Calories do matter, and weight loss is a result of tilting energy balance in favor of expenditure, succeeding at that task is complex and multifactorial. Using nutrient dense foods that help people feel fuller longer, may promote good health and an appetite that is easier to manage.

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References

(1) Bray G and Champagne CM, Beyond Energy Balance: There Is More to Obesity than Kilocalories, J Am Diet Assoc. Volume 105, Issue 5, Supplement, Pages 17-23 (May 2005).
(2) Nutrition Business Journal, 2009 Sports Nutrition and Weight Loss Report 
(3) Dansinger ML , Gleason JA , Griffith JL , Selker HP , Schaefer EJ . Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction (A randomized trial). JAMA . 2005;293:43–53 .
(4) Leidy HJ, Carnell NS, Mattes RD, Campbell WW. Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women. Obesity (Silver Spring). 2007 Feb;15(2):421-9. Leidy HJ, Carnell NS, Mattes RD, Campbell WW. 
(5) Paddon-Jones D, Westman E, Mattes RD, Wolfe RR, Astrup A, Westerterp-Plantenga M. Protein, weight management, and satiety. Am J Clin Nutr. 2008 May;87(5):1558S-1561S. 
(6) Kong AP, Chan RS, Nelson EA, Chan JC. Role of low-glycemic index diet in management of childhood obesity. Obes Rev. 2010 Jul 21. [Epub ahead of print