Exercise Determinants of Weight Loss

Key Considerations for Metabolic Syndrome
and Diabetes Prevention Programs

Ralph La Forge, MSc
Duke University Medical Center
Division of Endocrinology, Metabolism and Nutrition
Durham, NC

Attempting to estimate how much body weight someone will lose in response to an exercise program has never been easy. In fact - it is likely more of a roulette play than a precise determination. For example, many health promotion and exercise professionals utilize the 3500 kcal per pound of fat estimation, i.e., one-pound of weight loss or at least fat weight loss in response for every 35 miles of running or walking based on the assumption of each mile is worth an estimated gross energy expenditure of 100 kcal per mile. This assumption while still a reasonable teaching tool will most often underestimate actual weight loss. An energy deficit or expenditure of 3500 kcal causes more than 1 lb of weight loss owing to the oxidation of lean tissue and associated water loss.

This paper will address exercise-generated weight loss factors principally for those who are at risk for cardiometabolic disease but particularly diabetes. The same considerations discussed here clearly apply to those with type 2 diabetes where therapeutic weight loss has been difficult to achieve however there are additional pharmacotherapeutic and metabolic factors that impact exercise-generated weight loss success with this population. This topic has been recently and expertly addressed elsewhere (Pi-Synyer 2005).

Practically then what then should health care professionals expect for exercise-generated weight loss and how should we estimate weight loss in response to physical activity programs especially for those with prediabetes and the metabolic syndrome? What are the fundamental exercise-related considerations that determine energy expenditure and weight loss in adults? Essentially there are two divisions of considerations: exercise-related factors and non-exercise related factors. The following is a brief review.

Exercise related factors

1. NET VS GROSS ENERGY COST OF THE ACTIVITY

When body weight loss is the primary outcome then the person prescribing the program must calculate or at least estimate the net energy cost of the activity. The net cost of the total activity program will better represent the energy expenditure that is devoted directly to exercise fuel utilization, e.g., fat. Net energy cost is differentiated from the gross energy cost of the activity. The net cost of exercise is the exercise energy expenditure minus resting energy expenditure or minus what you would have been doing anyway, e.g., sitting around, if you did not choose to exercise during that time. Activities that require a lower rate of energy expenditure and that take more time to complete, for example walking at a moderate pace (2-3.5 mph), there will be a greater disparity between gross and net energy expenditure on a per mile of walking basis.

For example, during a two-mile walk, the difference between gross and net energy expenditure is greater at the slower walking speeds because more time is being displaced from what a person would have been doing anyway should they have chosen not to walk during that time. At 2.5 mph a two mile walk for a 160 lb person the gross cost would be 168 kcal but the net cost would be 112 kcal (reference tables in Howley & Franks 2007, La Forge 2003). As walking speed increases (less time per mile), say greater than 4 mph, the gross cost begins to better approximate net cost. The gross cost includes the walking energy expenditure but does not factor out what they would have been doing anyway during that time. Think of the net cost as being the actual added caloric expenditure of an exercise program to your daily living routine. This would be important to know when attempting to predict actual weight loss. See BOX below for an example.

2. DURATION and INTENSITY OF PHYSICAL ACTIVITY

The total duration of time and the rate of energy expenditure are prime factors in determining the oxidation of fat stores which ultimately lead to fat weight loss. In the 1970's the American College of Sports Medicine developed a series of simple equations to estimate the "steady-state" energy requirement of many common activities, e.g., walking, running cycling etc. Although these equations are instructive in demonstrating the relationship of time, exercise load, and velocity to caloric expenditure they are not very time efficient for day to day use for individual clients. These equations are programmed equitably in many stationary exercise machines and reflect an acceptable approximation of the actual gross energy expenditure of cycling, treadmill walking/running, or stepping. For practical purposes one can also approximate the energy expenditure of a given activity by knowing the relative intensity of the activity (e.g. speed of walking), exercise time in minutes or hours, and the individuals body weight if the activity is weight bearing. There are numerous reputable publications that publish approximate energy cost calculations and/or tables of various activities (ACSM 2006, Howley 2007, ACE 2003). But knowing the caloric cost of exercise and using this information to estimate body weight loss is still only moderately related to how much actual body weight someone will loose in response to a 10-week walking program for example. You might walk 20 miles a week at a gross caloric cost of 2,000 kcal 20,000 total kcal for the 10 weeks and loose three, six or ten pounds. Dividing the 20,000 kcal would predict ~5.5 pounds of fat loss but that would assume that you spent exactly 20,000 kcal and that six fat pounds would generate exactly six pounds of actual body weight loss. Not likely.

Do Pedometer Step Counts Predict Weight Loss?

Pedometry (the use of walking step counters) or walking step-counts has recently been used as an acceptable estimate of walking energy expenditure. Many pedometers are programmed to estimate energy expenditure based on body weight and step count. Portable accelerometers (more advanced pedometer devices) estimate energy expenditure more reliably than simple step-only counting pedometers but still are only good approximations of actual energy cost.

It is important here to note that step-only devices (e.g., New Lifestyles SW-200 or Accusplit's Eagle 120 XL or Eagle 2720) are most relevant for diabetes prevention and diabetes management programs. Step only pedometers are most reliable at measuring steps. This is in contrast to pedometers that grossly estimate distance and caloric expenditure. Step-count is the primary physiologic variable for cardiometabolic outcomes. Each walking step an insulin sensitizing PPAR activating, muscular contraction which contributes to improved insulin sensitivity, blood lipid control and fat weight loss.

As a general rule, ~2000 steps with a step-only pedometer is equivalent to approximately one-mile which is approximately 100 kcal of gross energy expenditure for individuals who are within 10-20 lbs of their ideal body weight. Of course those that have significantly higher body mass indices (eg. BMI >35) the gross caloric cost per mile is greater (~120-150 kcal per mile) in proportion to their body weight. Past research has demonstrated that at least 10,000 steps per day is required for overall cardiovascular and metabolic health and 12,000 - 15,000+ steps per day for weight loss programs (Tudor Locke 2003) is required.

3. MODE or NATURE OF PHYSICAL ACTIVITY

The more muscle fibers and muscle groups that are involved in a given effort the greater the metabolic energy required. Cross country skiing, long-distance running, intense dance exercise, heavy physical labor, and some forms of hatha yoga sequences, for example, require more energy expenditure if they are sustained for more than two or three minutes than similar efforts that utilize a smaller proportion of available muscle mass, e.g., stationary cycling, resistance training on an isolated muscle group. Gravity also imposes greater energy expenditure for a given duration of weight bearing exercise. For example, variable-terrain walking or hiking at 3 mph will expend more calories than walking the same course on flat terrain. Even when considering the lesser energy requirements of the downhill segment of walking a loop course - the total energy expenditure will be somewhat greater when hills are included.

Non-weight bearing activities such as cycling and swimming generally expend fewer calories for a given effort level because there is less gravitational stress on the major muscle groups. On the other hand, because there is less repetitive stress on weight bearing joints, cycling and swimming can be tolerated for longer periods of time which may allow these to match or exceed the total energy cost of more intensive weight bearing exercise such as running.

4. MUSCLE MASS AND BODY WATER CHANGES

Exercise programs which impose significant resistive loads, e.g., resistance exercise training, may actually increase muscle mass by several pounds which can partially offset decreases in adipose tissue volume. Even sedentary overweight individuals who begin a walking program can gain some lean muscle weight in muscle groups which support walking mechanics. Likewise, backpacking over variable terrain with a heavy pack load can expend significant energy but it can also increase vertebral and flexor and extensor muscle mass of the lower extremities. Also understand that early changes in body weight can be attributable to changes in body water as well as reductions in body fat.

5. EXERCISE ECONOMY (mechanical efficiency)

Those who are unskilled or utilize unnecessary movements during physical activity will expend more calories for a given duration of activity. This may sound advantageous but the flip-side of this is that this inefficiency increases both metabolic fatigue (higher oxygen costs and heart rates) and reduces exercise time. Such movement inefficiencies increase musculoskeletal stress and proneness to overuse injury. Running is a good example of an activity that takes time to improve efficient running mechanics that help reduce unnecessary musculoskeletal stress. The energy cost of wasteful and unnecessary arm and lower-limb movements while running a given distance divert energy from the objective of the activity itself, i.e. running a given distance. Swimming is another activity that requires a significant amount of mechanical efficiency or "motor coordination" to improve one's ability to sufficiently prolong swimming time. In other words, those who are more efficient swimmers swim longer and faster and thus expend more calories (body density and buoyancy also affect the energy cost of aquatic exercise). Health professionals should understand that exercise economy does improve over time and aids in the prolongation of activity, thus, a greater total energy expenditure.

6. EXCESS POST EXERCISE ENERGY EXPENDITURE

It is problematic and impractical to assign the "post-exercise burn" as a prime factor in influencing exercise-associated weight loss because of the complexity of the metabolic variables that determine post exercise caloric expenditure. Some fitness professionals assign great meaning to the excess post workout oxygen consumption (EPOC) but it is difficult to rationalize that the added caloric expenditure is sufficient to significantly impact weight loss over a relatively short period of time, e.g., three months. Studies do show that this effect exists after both aerobic and resistance exercise. Without question, aerobic exercise burns more calories during exercise when compared to resistance training when compared by duration and intensity even though this difference is partly offset by the higher increase in caloric expenditure that occurs during the EPOC phase after resistance or anaerobic exercise. There is also evidence that fat oxidation is a major contributor to EPOC energy expenditure (Calvin 2005). Depending on the mode, intensity and duration of the exercise session EPOC caloric values can be anywhere from 10 - 150 kcal over the next 12-24 hours. The duration and intensity of exercise to generate 24-hour EPOC's greater than 100 kcal is generally beyond what most nonathletic individuals will tolerate. Over time, say 2-5 years, the more moderate EPOC's can certainly have a cumulative effect on energy balance and result in fat weight loss. But again - I don't think that this should be overly emphasized with recommendations made to overweight clients because the primary predictor of weight loss is the activity session itself.

Resistance Exercise and Excess Caloric Expenditure

In their 2004 survey of the relevant literature, Meirelles and Gomes (Meirelles 2004) found that excess post oxygen consumption (EPOC) resulting from a single resistance exercise session does not represent a great impact on energy balance but its cumulative effect may be relevant. This is echoed by Reynolds and Kravitz (2003) in their survey of the literature where they concluded that the overall weight-control benefits of EPOC, for men and women, from participation in resistance exercise occur over a significant time period, since kilocalories are expended at a low rate in the individual postexercise sessions.
What is clear is that the EPOC effect is greater the greater the intensity of the exercise and the greater the time spent during the exercise phase. Most studies found a linear relationship with time of exercise and the effect. One found a curvilinear relationship between the intensity and the EPOC effect, though others found a linear relationship.

Non-exercise Related Factors

1. BODY MASS.

Sustained activities that require the individual to carry their own weight while performing the conditioning activity will require higher caloric costs. Walking, running, hiking, dancing, stair stepping, domestic household/yardwork chores are good examples of weight-bearing activities. In contrast, aquatic activities where there is total or near total water emersion will lessen the energy expenditure for a given perceived effort. Likewise, cycling (stationary or supine) and exercise on machines that infer a mechanical advantage for walking, running or stepping motions will lessen energy expenditure compared with those that require complete utilization of your body mass and exercise mechanics. This in no way reduces the many other benefits of mechanically assisted exercise such as that executed on the many varieties of exercise machines - in some ways the mechanical advantage some machines invoke enhances exercise comfort and reduces impact and musculoskeletal stress. There is also the direct effect of weight loss itself. As one looses weight resting and nonresting energy expenditure begins to drop because less mass is being moved around, requiring less effort to carry it (Heshka,1990).

2. ENERGY COMPENSATION AND CONSERVATION

Quite obviously - daily energy intake will markedly influence energy balance and weight loss. Some of us find that over the course of a day we increase caloric intake when we start an exercise program. Perhaps as many as 20% of adults actually compensate a 300 kcal workout with a 300 kcal of additional food intake over the next 24 hours. Still others find that vigorous endurance exercise when perhaps timed before lunch or dinner decrease caloric intake or actually conserve energy intake over a 24 hour period. Additionally, some of us decrease energy expenditure over the course of the day by nearly same amount of energy required for the exercise session itself. If you exhaust yourself with a 45-minute hilly run and subsequently reduce the level and number other daily activities more than you would have done otherwise this will, over time, reduce the net effect of exercise on weight loss.

Perhaps the most telling indicator of exercise-generated weight loss is total daily energy expenditure. For example, when someone adds a 500 kcal workout to a given day's energy expenditure does this mean that they can actually add 500 kcal to their total daily caloric expenditure? Answer, it depends on what they did with the rest of their day. If the 500 kcal workout was exhaustive such that they reduced their other daily activities by 200 kcal, say because they took a long nap or relaxed in the recliner for an extra 90 minutes, the answer is no. In this case the actual added energy expenditure to the daily routine was only a net 300 kcal. Prolonged intensive workouts for many people tends to favor a reduction in routine daily physical activities by some measure principally because they are tired or lack the stamina to carry on usual activities for 2-6 hours after the prolonged workout.

3. METABOLIC PHENOTYPE and GENOTYPE

Heritable factors affect exercise weight loss responsivity to some degree. Resting metabolic rate, adipokine production, leptin deficiencies, muscle fiber type, and nutritional genomics all influence fat and carbohydrate metabolism and ultimately weight loss. For example, variation in the perilipin gene appears to render some people resistant to weight loss from calorie restriction by inhibiting a fat burning enzyme (hormone-sensitive lipase). Perilipin acts by preventing a "fat-burning", hormone sensitive lipase, from entering fat cells where it can break down fat molecules and convert them to energy. This process can, at least in theory, subdue fat metabolism during exercise.

Muscle fiber type (e.g. slow and fast twitch) which is largely determined by genetics has also been shown to influence weight gain and weight loss (Karjalainen 2006). Greater weight gain in subjects with a relatively low percentage of type-I skeletal muscle fibers may be linked to the hampered ability of skeletal muscle to oxidize lipid. Weight loss interventions have been more successful in obese women with a higher percentage of type-I muscle fibers compared with those having a lower percentage.

Hypothesized defects in mitochondrial function, the organelles that provide energy to the muscle cell, in those with insulin resistance may explain why some patients with type 2 diabetes have less response to intensive aerobic exercise than healthy normals. Peterson and coworkers at Yale (2004) have elegantly shown that insulin resistance in the skeletal muscle of insulin-resistant offspring of patients with type 2 diabetes is associated with dysregulation of intramyocellular fatty acid metabolism, possibly because of an inherited defect in mitochondrial oxidative phosphorylation.

4. GENDER DIFFERENCES IN FAT STORAGE AND METABOLISM

There are gender differences in fat storage and utilization which can influence exercise associated fat weight loss in women. This does not mean that women will not loose body weight with exercise but gender differences in fat storage and metabolism may alter the fuels used for exercise and possibly the rate of actual weight loss. The following summarizes these differences (Wajchenberg 2000):

1. Lipid accumulation is favored in the femoral region of premenopausal women in comparison with men the same age

2. There appears to be a relative resistance to abdominal visceral adipose tissue reduction in obese women compared to men. Where absolute and relative reductions in body weight and body fat are similar, men mobilize more intra-abdominal fat than women, whereas women lose more subcutaneous fat. The greater reduction in intra-abdominal fat seen in men is accompanied by a more pronounced improvement in the metabolic risk profile (Wirth 1998).

Much of the current research is reporting that the proportion of energy derived from fat is increased during low to moderate intensity exercise in women as compared to men however this should not be construed as meaning that this metabolic feature is associated with more actual body weight loss.

Exercise Volume and Weight Loss Maintenance

Another issue is how much physical activity energy expenditure is required to maintain weight loss once weight has been lost. Only in the past decade did investigators begin to investigate how much exercise is required to maintain weight loss over the long term. Klem and colleagues (Keim 1997) performed a retrospective analysis of the exercise habits of subjects in the National Weight Control Registry and found that those persons who successfully maintained long-term weight loss reported an energy expenditure of 2800 kcal/wk. Other studies have also shown that individuals who successfully maintain large weight loss over at least a year have typically performed 7 h/week of moderate- to vigorous-intensity exercise (Weinsier, 2002). This seems a considerable volume perhaps exceeding the weekly physical activity volume that was required for the initial weight loss.

Additional Considerations

The American College of Sports Medicine recommends at least 1000 - 2000 kcal of physical activity per week for weight loss. Other authorities recommend a higher weekly volume of exercise for weight loss, e.g. 2500 kcal per week (Jeffrey, 2003) or at least one-hour per day every day. Such published values generally represent gross energy expenditures. For reasons stated earlier these gross cost values will somewhat overestimate the actual added energy expenditure devoted to the oxidation of fat and carbohydrate stores and thus weight loss. This overestimation is probably small but over time it could be a factor in predicting fat weight loss.

In the end - it is still difficult to determine precisely how much body weight a given individual will loose in response to a known volume of exercise. Still, it is reasonable to estimate fat weight loss by approximating the energy cost of exercise from ACSM energy cost equations and/or tables which base caloric expenditure on exercise frequency, intensity, duration and, when applicable, body weight. But this method will only moderately parallel actual body weight loss for an exercise program of given duration. Clearly, the most successful programs for long-term weight control have involved combinations of diet, exercise, and behavior modification (Wing, 2002). Exercise alone, without concomitant dietary caloric restriction and behavior modification, tends to produce only modest weight loss of 3-5 lbs. The optimal volume of exercise to achieve sustained weight loss is probably much larger than needed to achieve improvements in cardiovascular and metabolic health, i.e. reduction in the risk for cardiovascular disease and diabetes.

So how should we proceed in estimating weight loss with exercise programs?

First, appreciate the complexities of training and heritable factors that influence weight loss and exercise. Understand that every pound that is lost is not necessarily fat but can reflect body water changes. Secondly, understand when published gross energy costs of exercise may over-represent energy devoted to weight loss. Third, improve your skills at estimating the caloric cost of a variety of weight-bearing and non-weight bearing exercise routines. Finally, respect how energy conservation and compensation can influence weight loss outcomes.

Perhaps the real value in appreciating the complexity of these exercise and non-exercise related factors is to not to discourage clients progress by making precise predictions of weight loss. Do not oversell weight loss as the primary rationale for adopting a physical activity program. Help your patients be mindful of the fact that physical activity clearly can be of great insulin sensitizing, cardiorespiratory and even spiritual value with or without changes in body weight.

References:

ACE Personal Trainer Manual, 3rd Edition. (C Bryant & D. Green editors) ACE, San Diego, 2003

ACSM Guidelines for Exercise Testing and Prescription, 7th Edition, (M Whaley editor). Lippincott Williams and Wilkins. Philadelphia, 2006.

Calvin C. Kuo CC, Brooks GA et.al. Lipid oxidation in fit young adults during postexercise recovery. Journal of Applied Physiology 2005;99:349

Heshka S, Yang MU, Wang J, Burt P, Pi-Sunyer FX: Weight loss and change in resting metabolic rate. Am J Clin Nutr 1990;52:981-986.

Howley E. and Franks D. Health and Fitness Instructors Handbook, 3nd edition. Human Kinetics, Champaign IL. 1997.

Howley E and Franks D. Health and Fitness Instructors Handbook, 5th edition, (Chapter 4) Human Kinetics, Champaign IL. 2007.

Jeffery RW, Wing RR, Sherwood NE, Tate DF: Physical activity and weight loss: does prescribing higher physical activity goals improve outcome? Am J Clin Nutr 2003;78:684-689.

Karjalainen J et.al. Muscle fiber-type distribution predicts weight gain and unfavorable left ventricular geometry: 19 year follow-up study. BMC Cardiovasc Disord. 2006; 6: 2.

Klem ML, Wing RR, McGuire MT, Seagle HM, Hill JO. A descriptive study of individuals successful at long-term maintenance of substantial weight loss. Am J Clin Nutr 1997;66:239-46

La Forge R. Cardiorespiratory Fitness. In: ACE Personal Trainer Manual. 3rd Edition. 2003. American Council on Exercise, San Diego.

Meirelles, C and Gomes, P. (2004). Acute effects of resistance exercise on energy expenditure: revisiting the impact of the training variables. Rev Bras Med Esporte Vol.10, No 2 Mar/Apr 2004.

Pérusse L., Bouchard C et.al, The Human Obesity Gene Map: The 2004 Update Obesity Research 2005;13:381-490.

Petersen, KF et. al. Impaired Mitochondrial Activity in the Insulin-Resistant Offspring of Patients with Type 2 Diabetes, NEJM 350:664-671, 2004.

Pi-Sunyer FX. Weight Loss in Type 2 Diabetic Patients Diabetes Care 2005;28:1526-1527.

Renolds JM and Kravitz L. Resistance training and EPOC. On-line review. http://www.unm.edu/~lkravitz/Article%20folder/epoc.html

Tudor-Locke C. Manpo-Kei: The Art and Science of Step Counting. Trafford Publishing, Victoria Canada. 2003.

Wajchenberg BL Subcutaneous and Visceral Adipose Tissue: Their Relation to the Metabolic Syndrome. Endocrine Reviews 2000;21;697-738

Wing RR: Exercise and weight control. In Handbook of Exercise in Diabetes. 2nd ed. Ruderman N, Devlin JT, Schneider SH, Kriska A, Eds. Alexandria, VA, American Diabetes Association, 2002, p. 355-364

Weinsier RL, Hunter GR, Desmond RA, Byrne NM, Zuckerman PA, Darnell BE: Free-living activity energy expenditure in women successful and unsuccessful at maintaining a normal body weight. Am J Clin Nutr 2002;75:499-504.

Wirth A and Steinmetz B. Gender differences in changes in subcutaneous and intra-abdominal fat during weight reduction: an ultrasound study. Obesity Research 1998;6:393-399

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