|Energy Balance Update: Keep Moving!
Len Kravitz, Ph.D.
Hall, K.D., Heymsfield, S.B., Kemnitz, J.W., Klein, S., Schoeller, D.A., and Speakman, J.R. (2012). Energy balance and its components: implications for body weight. American Journal of Clinical Nutrition, 95, 989-994.
Esteemed researchers representing the American Society of Nutrition and the International Life Sciences Institute recently converged to summarize the state-of-the-art research on energy balance as it relates to weight management. Key questions addressed in their published consensus statement and discussed in this column are 1) an explanation of energy balance and imbalance in regards to energy intake and energy expenditure change over time, 2) a discussion of the interactions between the components of energy balance and how are they are regulated, 3) the efficacy of currently held popular beliefs on energy balance, and 4) the limitations facing researchers on energy balance.
The Energy in The Foods We Eat
The dietary foods eaten that provide energy for life and calories to a person's weight include fat, protein, carbohydrate and to some degree alcohol. As small as ~2 to 10% of this total intake will become waste to the body and be excreted. The remaining foods eaten are absorbed and biologically broken down (or oxidized) for energy needs of the body, including growth, cell maintenance, physical activity, pregnancy and lactation, and other cellular life processes (Hall et al, 2012). The caloric yields for fat (9 kcals/gram), carbohydrate (4 kcals/gram) and protein (4 kcals/gram) refer primarily to the amount of fuel available from these fuels that the body cells can use for physiological processes. Some foods depending on their type of fiber content are not digestible by the body and thus not absorbed and utilized by the body. As well, food preparation measures may also inhibit the actual absorption of a food, and thus the amount of calories into the body.
What are REE, TEF and AEE?
Common energy balance components of interest in weight management include REE, TEF and AEE. Resting energy expenditure (REE) is the non-exercise energy needed throughout the day to stay alive. It represents 2/3 of the energy needs of the body. It varies widely between people due primarily to body composition (fat versus muscle on the body) and body size (the greater the body mass area, the greater the REE to stay alive). Interestingly, the brain, heart, kidney and liver, which weigh relatively small amounts of weight demand significant energy for life, and contribute meaningfully to the body's total REE. As well, scientists believe approximately 250 kcals/day of REE is not fully explained how it relates to differences or variability between people (Hall et al., 2012). The TEF or thermic effect of food is the energy expenditure associated with processing and digestion of foods eaten. Dietary composition of protein elicits the highest effect of TEF, which is followed by carbohydrate and then fat. Activity energy expenditure (AEE) is the fuel utilized by the body via structured exercise and non-exercise movement (such as shopping, moving, doing daily chores and fidgeting). Perhaps the greatest range observed in people is with AEE, as many people move a lot during their waking day and do a considerable amount of daily exercise, while others live primarily sedentary lifestyles.
How Much Energy Does the Human Body Store?
On average, the human body stores 130,000 kilocalories of fat, primarily in the form of triglycerides. According to Hall et al. (2012) a lean adult may have ~35 billion adipocytes (fat cells) as compared to an extremely obese individual who may have 140 billion adipocytes. Carbohydrate is stored in the form of glycogen, which is bound to water, in the liver and muscle. Changes in carbohydrate storage often result in meaningful shifts in fluid storage; the more carbohydrate eaten and stored, the greater fluid retained by the body. Fat, contrariwise does not need any water to bind with it for storage in the body and protein needs very little water for storage. Therefore, a person eating a higher percentage of carbohydrate, and not necessarily greater kilocalories, will retain more water, thus increasing total body weight (due to the increase in water retention).
The Regulation of Energy Expenditure Picture
Is there a Set Point?
A positive energy balance refers to a person taking in more kilocalories than expending. Over time, a positive energy balance will result in overweight and/or obesity. The interaction of REE, TEF and AEE may be affected if a person is in a positive (weight gain) or negative (weight loss) kilocalorie consumption mode. Presently, scientist feel the body has a 'set point' or 'setting point' to regulate body weight (Hall et al., 2012). The 'set point' theory suggests there is a highly organized feedback control system in the body that tries to best regulate food intake and energy output. The 'setting point' theory suggests the body regulates energy intake and output with a less orderly feedback system. Indeed, the actual regulation of energy storage on the body is still under intense investigation by scientists and may be a combination of both theories. Interestingly, due to daily changes in energy intake (meals we eat) and energy output (activity and exercise), Hall and colleagues note that humans are regularly in a state of energy imbalance (i.e., going back and forth from positive to negative).
How Do We Know When to Eat and When to Stop Eating?
The feeling of fullness from a meal, referred to as satiety is determined by the body due to sensory receptors, noting an enlargement of the gastrointestinal tract, sending a message to the brain the stomach is full. Other specialized intestinal hormones also translate and send 'feeling full' messages to the brain. Between meals the intestines will start to secrete the hormone Ghrelin. As secretions of Grehlin increase there is a positive messaging system sent to the brain to eat, thus Ghrelin is the hormone that signals it is time to eat. As Hall et al. (2012) continue, many people are highly affected by cognitive stimuli (such as commercials and advertising), which stimulates food intake, regardless whether the body is in need of foodstuffs for energy.
Where Does Exercise Fit Into the Energy Balance Equation?
A major part of creating a negative energy balance (to lose weight) is the addition of exercise to a person's daily life. However, Hall et al. (2012) note that with some people adding extra physical activity during certain parts of the day leads to less activity during other parts of the day. This scientific knowledge is extremely useful to personal trainers designing weight loss exercise programs. Physical activity program designs need to be include ways to help clients more throughout the day as well as structured exercise. Hall et al observe that some studies show individuals may expend up to an additional 500 calories per day doing spontaneous movement.
Questions and Answers on Energy Balance
A. Is the customary weight management plateau observed after 6 to 8 months of a weight management due to a 'slowed metabolism'? Hall et al. propose that the research indicates this is more attributable to a failure to comply appropriately with the diet.
B. Are some people obese due to having 'slow metabolisms'? Hall et al advise this concept is typically not true. If a balance is not met by an individual with food intake matching energy output, this disproportion will result in weight gain (if intake is greater) or weight loss (if physical activity is greater).
C. Should exercise professionals still use the '3,500 kilocalorie rule to lose a pound of body fat'? The consensus panel suggests this rule is incorrect because no time period has ever been associated with this particular type of intervention. Most people vary widely in how the body will adjust to reduced caloric intake and increased energy output. Hall and colleagues note that the traditional '3,500 kilocalorie rule to lose a pound of body fat' represents a linear association of weight loss that isn't accurate with most people. Some people will lose a meaningful amount of muscle mass during caloric restriction only diets, which will have an also have a direct effect of metabolism. The panel suggests that consistent small changes, with decreases in energy intake and increases in energy output over time will yield realistic and positive changes in weight management.
Future Directions in Energy Balance
Energy balance is a complex integration of several bodily mechanisms (See Figure 1). Up to now, long sustained studies studying this phenomenon have not been completed. Eventually, when scientists develop new methodologies to study long-term energy balance, many of the unanswered questions pertaining to successful weight loss may be answered.
Exercise and Spontaneous Physical Movement are INTERRELATED with Diet and Eating Behaviors which are INTERRELATED with REE and TEF. All effect one another in some form or capacity.
Figure 1. Complex Interactions Affecting Energy Balance
Adapted from Hall et al., 2012
@bio:Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and was chosen as the American Council on Exercise 2006 Fitness Educator of the Year.