Understanding calories
Calories - energy balance & energy availability
This will take 6 minutes of your time.
What are calories?
Like a gram is a measurement of weight, calories are a measurement of energy. Calories express the quantity of energy (heat) needed to raise 1ml of water by 1 °C.
Why speak about calories?
During the Christmas and New Year period people often are conscious of gaining weight and more specifically fat. This news letter will explain a basic understanding of calories.
Gaining and losing weight is simple math.
First we need to understand energy balance and energy maintenance. Yes, there is a difference.
Energy availability is the residual energy left over (relative to lean body mass i.e. muscle mass) for healthy, physiological function, once the difference between energy expended from exercise minus energy consumed has been accounted for. If energy availability drops below 30 calories per kilogram of lean body mass, a plethora of negative physiological and psychological effects will likely occur. Optimal energy availability for females is believed to be 45 calories per kilogram of lean body mass, whilst with males optimal energy availability is 40 calories per kilogram of lean body mass as men need less energy to maintain homeostasis. (“Energy Availability in Athletics: Health, Performance and Physique” by Melin AK, Heikura IA, Tenforde A, Mountjoy M, International Journal of Sport Nutrition and Exercise Metabolism © 2018 Human Kinetics, Inc.)
Energy balance does not always result in adequate physiological functions. Due to the metabolism becoming constrained during intense exercise, an individual might appear to be in energy balance and weight stable, with total daily calorie intake and total daily energy expenditure being matched. However due to the constraining effect of metabolic adaptation (the body's ability to reduce energy expenditure due to being in a low energy state), an individual may appear to be weight stable but that does not mean the individual is healthy due to suppressed reproductive functioning, suppressed resting metabolic rate (metabolism), non-exercise thermogenesis (body heat), reduced thermic effect (energy for digestion) of food and other physiological factors e.g. muscle protein synthesis is compromised to compensate for low energy availability. Another example is lack of menses in females; it's not the stress of the exercise driving the lack of menses but the lack of energy available to support maintenance of normal physiological function.. (Journal of Sports Sciences, 2011; 29(S1): S7-$15)
Basically, your body adapts to less energy by turning “off” certain functions, so what was once a deficit to lose weight is now no longer a deficit and weight gain then occurs. To lose weight, you might need to eat less but to get lean you need to eat more. For a better explanation of this, sign up to my coaching ;)
Energy balance = (energy intake – energy expenditure) / lean body mass.
Should I restrict all my calories after Christmas and New Year?
In obese populations, aggressive caloric restriction is a potentially powerful intervention since a greater initial weight loss is associated with greater long-term success in weight loss maintenance (Nackers L, Ross K, Perri M. The association between rate of initial weightloss and long-term success in obesity treatment: does slow and steady winthe race? Int J Behav Med. 2010;17(3):161–7). However, a meta-analysis by Tsai and Wadden (Tsai A, Wadden T. The evolution of very-low-calorie diets: an update andmeta-analysis. Obesity (Silver Spring). 2006;14(8):1283–93) found that Very Low Energy Availability (VLED) did not result in greater long-term (1 year or more) weight loss than Low Energy Dense (LED i.e. low calorie dense). Eight to 12 week VLED are common in clinical practice before transitioning to less severe caloric restriction; however, there is an ongoing debate regarding the duration that can be safely sustained for VLED. Multiple deaths have been reported due to low-quality protein intake, excessive loss of lean mass, and inadequate medical supervision (JE D, J J, S G. Diet and body composition. Effect of very low calorie dietsand exercise. Sports Med. 1991;12(4):237–49).
Adverse effects of VLED include cold intolerance, fatigue, headache, dizziness, muscle cramps, and constipation. Hair loss was reported to be the most common complaint of extended VLED use. It should be noted that VLED use has limited relevance to healthy and athletic populations. (Saris W. Very-low-calorie diets and sustained weight loss. Obes Res. 2001;9Suppl 4:295S–301S)
Common Mistakes
When trying to lose weight, people make the following common mistakes:
· Trying to lose weight too rapidly. Most people are impatient about weight loss. They want to see results within a couple of weeks, but unfortunately this expectation is not realistic. Although rapid weight loss is possible, this reduction is mostly dehydration, which reduces performance and the ability to train. Weight loss without performance loss has to occur slowly. When weight loss is more than 0.5kg per week, majority of the weight loss is also from muscle which is expensive and difficult to achieve so should not be compromised unless health is an extreme concern.
· Trying to lose weight during a muscle building phase. People often try to lose weight when desperately trying to gain significant muscle, and this effort may result in underperformance. Because hard training is difficult when the energy intake is reduced, weight loss is best accomplished during a phase where muscle building is not prioritised.
· Not eating breakfast or lunch. Another weight-loss approach that people have tried is skipping breakfast and sometimes skipping lunch.
Although this approach may work for some, it increases hunger feelings later in the day, and one large evening meal can easily compensate for the daytime reduction in food intake. In addition, exercise capacity and the ability to train may decrease without breakfast because glycogen stores (fuel for the muscles) may be low.
· Taking in too little carbohydrate. When losing body weight (being in negative energy balance), people also risk losing muscle mass.
This risk can be reduced by consuming relatively large amounts of carbohydrate. Carbohydrate intake has a protein-sparing effect (carbohydrates reduce the chances of losing muscle because your body’s preferred source of fuel is carbs).
(Mettler et al. 2010)
Are all calories the same?
Yes and no. It depends who you are talking to. A calorie is a calorie, like a gram is a gram or a meter is a meter. However, not all proteins, carbs and fats have the same calories.
Let me explain:
Kcal = calories
Carbohydrate, fat, and protein can all provide energy but the amounts of energy they deliver are different.
· The energy content of carbohydrate depends on its type and on the arrangements of atoms within it. The combustion of glucose, for instance, gives 3.7 kcal/g, whereas the combustion of glycogen and starch is about 4.2 kcal/g. The latter figure is normally used as the energy value of carbohydrate (1 g carbohydrate = 4.2 kcal).
· The energy content of fat also depends on the structure of the triacyglycerol or Fatty Acid (FA i.e. the fat your body uses as a fuel). A medium-chain FA, such as octanoate (eight-carbon FA), may contain 8.6 kcal/g, whereas a long-chain FA may contain up to 9.6 kcal/g. The energy content of fat in the average diet is 9.4 kcal/g.
· The energy content of protein depends on the type of protein and the nitrogen content (proteins have nitrogen bonds).
· Nitrogen does not provide energy; therefore, proteins with higher nitrogen densities contain less energy per gram. The nitrogen content in foods may vary from 15% (whole milk) to approximately 19% (nuts and seeds).
· The energy content of protein in the average diet is 5.7 kcal/g.
Sometimes food is not completely absorbed. Incomplete digestion and absorption will, of course, result in decreased availability of energy. Wilbur Olin Atwater, one of the pioneers in studying human energy balance determined this fact. After measuring many kinds of foods, Atwater (an American chemist) came up with energy values for foods that accounted for differences indigestibility.
Conveniently, these energy values were rounded to whole numbers.The energy contents of carbohydrate, fat, and protein were 4 kcal/g, 9 kcal/g, and 4 kcal/g, respectively.
The percentage of food energy that is absorbed is often expressed in a coefficient of digestibility. A coefficient of digestibility of 50 means that only half of the energy ingested is absorbed. Adding fibre to a meal generally reduces the coefficient of digestibility. A smaller amount of energy is available to the body from a food item that is high in fibre than from a food item that has identical energy but is low in fibre. Fibre causes the food to move faster through the gastrointestinal system, which leaves less time for absorption. On average, 97% of carbohydrate is completely digested and absorbed. For fat, this value is 95% and for protein it is 92%.
The coefficient of digestibility of wheat-bran protein is only 40%, and its calorie contribution is just 1.82 kcal/g, which is significantly less than the 4 kcal/g. The coefficient of digestibility wheat bran carbohydrate is 56%, and its calorie contribution is only 2.35 kcal/g, which is again far less than Atwater's estimate of 4 calories per gram.
Basically - high fibre foods are good for keeping you full but also reduce the amount of calories you in theory will absorb from foods. This is a great technique for fat loss or maintenance.