The overweight and obese population in our country continues to increase, much as it is across the globe. Many factors, both genetic and environmental, have been implicated in this disease now reaching epidemic proportions. Many doctors, dietitians, obesity researchers and trainers have all at one time or another been led to believe that some overweight people are somehow resistant to weight loss even though energy intake is low.
This is typically blamed on three factors…
- Low thyroid function
- Genetically low basal metabolic rate (BMR)
- Low energy cost of movement or some combination of the above.
As trainers, it is vital that we understand how a person gains weight and the reasons for maintaining the weight.
Knowledge of this process will help us identify:
- How a client gained excess weight, even though they report a caloric intake that is very low (800-1200 calories).
- Why a client does not lose weight, even after reported caloric intake is lowered and energy expenditure is increased.
- How, after repeated adjustments of "energy in" (food) and "energy out" (exercise), the client still maintains their weight.
Understanding this information will allow trainers to identify client non-compliance, avoid the search for unfounded solutions to fat-loss plateaus, have confidence in their abilities, and increase their effectiveness when dealing with fat-loss clients.
No discussion on the subject of weight gain or loss would be complete without prefacing the information with a discussion of The First Law of Thermodynamics.
Simply put, the laws of thermodynamics govern how a system will react to changes in energy intake or energy output. For our purposes, energy is measured in calories (a measurement of heat). Energy in is the food we eat and energy out consists of our activities of metabolism (anabolism and catabolism) including work done on the environment (exercise, activities of daily living). The laws of thermodynamics, as applies to altering body composition, can be explained by the following three equations:
- If energy in = energy out, then there is no change in mass. For clients this would be called maintenance.
- If energy in < energy out, then there is a decrease in mass, or weight loss.
- If energy in > energy out, then there is an increase in mass, or weight gain.
It is vital that trainers understand these facts. The problems of those who are overweight and those who are obese are, simply put, rooted in energy imbalance. One does not spontaneously gain fat in an energy deficit. Likewise, one does not lose weight while in a caloric excess.
These are the very points that invalidate the fad diets and gym science that seek to confuse the issue of how weight is gained. Understanding the first law of thermodynamics, it becomes obvious that carbohydrates themselves do not make one fat, excess calories do, regardless of the macronutrient composition of the diet.
So how do the obese or overweight become this way? There are many proposed reasons, ranging from genetic (physiological and behavioral) and hormonal to psychological abnormalities that affect satiety and eating behavior. However, looking for the genetic link to obesity is akin to looking for a genetic link to lung cancer. If you did not smoke, no matter what your genetic blueprint is it would be almost impossible to develop lung cancer. Therefore, regardless of the problems that contribute to weight gain, the bottom line is that a person must consume more energy than they expend, resulting in calorie storage.
We will confine this discussion to the aforementioned purported reasons of how our clients gain weight and fail to lose it: impaired thyroid function, genetically low BMR, and low energy cost of movement.
Impaired Thyroid Function
A low T3 output could certainly lead to a lower resting metabolic rate. Also, thyroid hormones are involved in normal adaptive thermogenesis, the raising or lowering of metabolic rate in response to overfeeding or caloric reduction. Impaired thyroid function could allow an individual to gain weight on fewer calories than would have been required had their thyroid functioned normally. If an individual has experienced an acceleration of weight gain or has had difficulty losing weight, it would be advisable for them to see their doctor to rule out the possibility of low thyroid output. If a low thyroid T3 level is diagnosed, the physician will prescribe synthetic thyroid hormone to bring levels within a normal range. During the period from diagnosis to finding the appropriate dose, weight loss may be a frustrating endeavor. However, most clients that present a history of thyroid insufficiency have been on medication for many years, and should therefore now have normal levels of thyroid hormones.
The erroneous assumption is that all cases, or even the majority, of weight-loss resistance are due to thyroid insufficiency. Studies of weight loss resistance often measure thyroid function and find no abnormalities. However, a few studies have shown a lower thyroid T3 level in some subjects with a genetic predisposition to obesity.9,10 These individuals had a three to eight percent reduction in resting metabolic rate (RMR). It is important to understand that even with a low thyroid output, a person will still lose weight when consuming fewer calories than they expend. The person with a lower T3 level attempting to lose weight may simply need to reduce calories and increase activity more than someone with normal thyroid function.
Genetically low BMR
Because obese and overweight individuals often report unusually low energy intakes that do not correspond with calculated energy expenditure, many look for a genetic component that would yield a decreased basal metabolic rate. Often a client will say, "I can’t understand why I’ve gained weight, I only eat 1000 calories a day," or "I only eat once or twice a day, yet I cannot lose weight."
Many studies have investigated the possibility that the obese have a lower BMR, making weight loss difficult. While there are those that do have several genetic factors conspiring to yield a lower metabolic rate, they are rare and relatively insignificant. The effect of this would be, at its greatest, a maintenance caloric level 100 to 200 calories less than predicted values. The preponderance of data available, however, suggests that obese individuals not only have a BMR similar to non-obese individuals, it may even be greater.
A 1986 study by Prentice, et al., concluded that, in regard to the obese women in their study, "…there was no evidence that their obesity was caused by a metabolic or behavioral defect resulting in reduced energy expenditure."6 The most noticeable difference between the obese and non-obese participants in this study was an underreporting of energy intake by the obese participants of about 837 kcal/day (more on this trend to follow).
Low energy cost of movement
With the low-BMR possibility not panning out, perhaps the energy cost of movement in the obese is low. This has been looked at also. Again, except for the infrequent occurrence of a true genetic abnormality, energy expenditure of movement for overweight individuals is normal, if not higher due to greater total body mass movement.5
Why can’t they lose weight?
It is unlikely that all of our difficult clients are afflicted with hypothyroidism, a genetically low metabolism, or a low energy cost of movement. Why then do they not lose weight? Why, after repeated reductions to their caloric intake and increases to their exercise prescription, do they not change?
Good questions, indeed. The answers lie in two widespread problems that occur with greater frequency and to a higher degree in people that are overweight and/or are interested in weight loss–Underreporting of caloric intake and overestimation of exercise performed.
Self-reported food intake is known to be an unreliable measure of energy intake in the overweight. A 1992 study in the New England Journal of Medicine illustrated this problem. The study looked at subjects that repeatedly failed to lose weight on self-reported caloric intakes of less than 1200 calories. Total energy expenditure (TEE) and resting metabolic rate (RMR) of the subjects were measured and found to be within five percent of predicted values, which was dramatically higher than the reported intake values. Additionally, no significant differences in thermic effects of food (TEF) or exercise energy expenditure between the weight loss resistant or normal obese were observed. Low energy expenditure was, therefore, excluded as a reason for self-reported diet resistance.
Why were these subjects resistant to weight loss? The researchers recorded an underreporting of actual food intake by 47 percent (+/- 16), and an over reporting of physical activity by ~50 percent. Based on this and other available data, a trend emerges: the higher one’s BMI and weight, the greater the degree of underreporting of caloric intake. If a comparison is made between data of reported caloric intakes and actual energy expenditure as measured by the doubly labeled water method (the most accurate available), an interesting picture emerges (Figure 1).
As the graph illustrates, the difference in reported intake in various studies from actual energy expenditure of typical persons at varying BMIs ranges from ~3 – 6 MJ/d (716-1200 kcal/d). Combine this with the typically lower daily activity levels of the obese and overweight and the shroud of mystery begins to lift. If the caloric intake were actually what had been reported, these subjects would have lost weight at record rates. But, the subjects were not losing weight, indicating that they were dramatically underreporting calorie intake. They are eating more, gaining weight and reporting less. Why did your client gain weight on a low calorie diet? Because they did not eat a low calorie diet. Why does their weight stay the same, even with a reduction of their caloric intake and increase their exercise volume? Because they are not reducing their caloric intake and they may be incorrectly reporting their volume of exercise. If they are accurate in their exercise reporting and are not changing their weight as you add more work, then they are simply eating more to compensate for the additional energy expenditure. These are the facts. What is the likelihood that fat-loss clients who never seem to change defy the laws of thermodynamics? None.
Plateaus, overweight, obesity and weight-gain problems are all caused by chronic or acute energy imbalances. For the vast majority of the personal trainer’s clients, genetic or metabolic disorders do not play a role in the inability to continue fat loss for those in need. Remember, the number of obese and overweight people in the U.S. is much higher than it was 10 years ago. This is not because of a dramatic shift in the gene pool.
Program compliance is the real problem. Behavioral and environmental conditions control a person’s ability to comply, including the simplicity of the program and how serious the triggering event was that led them to desire body-fat reduction. The conclusions reached in the meta analysis Energy Expenditure and Obesity sum this up quite nicely: "…contrary to many patient’s belief, there are no scientific arguments in favour of the existence of a "metabolic" type of obesity in which excess body weight would result from a deficiency in energy expenditure rather than from an excessive caloric intake."
- Buhl, KM, Gallagher, D, Hoy, K, Matthews, DE, Heymsfield, SB. Unexplained disturbance in body weight regulation: diagnostic outcome assessed by doubly labeled water and body composition analyses in obese patients reporting low energy intakes. Journal of the American Dietetic Association. 1995 Dec; 95(12): 1393-1400.
- Lichtman, SW, Pisarska K, Berman, ER, Pestone, M, Dowling, H, Offenbacher, E, Weisel, H, Heshka,S, Matthews, DE, Heymsfield, SB. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. New England Journal of Medicine. 1992 Dec; 327(27): 1947-8.
- Chernoff, R, St Jeor, ST (editors). Obesity Assessment: Tools, Methods, Interpretations. New York, NY. Chapman & Hall. 1997. p. 932 (pp. 192-201).
- Dalton S. Overweight and Weight Management. Gaithersburg, MD. Aspen Publishers. 1997. p. 615 (pp. 39-65).
- Balasse, E. Energy expenditure and obesity. Rev Med Brux, 1994; 15(4): 255-8.
- Prentice, AM, Black, AE, Coward, WA, Davies, HL, Goldgerg, GR, Murgatroyd, PR, Ashford, J, Sawyer, M, Whitehead, RG. High levels of energy expenditure in obese women. British Medical Journal. 1986 April; 292(6526): 983-7.
- Seidell, JC. Dietary fat and obesity: an epidemiological perspective. American Journal of Clinical Nutrition. 1998 March. 67(3S).
- Westerterp-Plantenga, MS, Fredix, E, Steffens, AB. Food Intake and Energy Expenditure. Boca Raton, FL. CRC Press. 1994. p.408 (pp. 235-257).
- Astrup, A, Buemann, B, Toubro, S, Ranneries, C, Raben, A. Low resting metabolic rate in subjects predisposed to obesity: a role for thyroid status. American Journal of Clinical Nutrition. 1996 Jun. 63(6): 879-83.
- Ranneries, C, Buemann, B, Toubro, S, Raben, A, Astrup, AV. Low energy metabolism in persons predisposed to obesity: significance of the thyroid status. Ugeskr Laeger. 1998 Jan 160(5): 644-7