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 Staff Update

Winter 2007

What's in the News?

Gaining Without Losing: The "Weight Loss-Independent" Health Benefits of Exercise

Glenn A. Gaesser, Ph.D.

Weight loss is routinely recommended for individuals considered overweight or obese, especially for those with type 2 diabetes and other weight-related health problems.1 Standard advice is to exercise more and eat less, with the assumption being that resulting weight loss confers all the health benefits.  Although weight loss can be achieved through exercise and calorie restriction, maintaining weight loss has proved to be a challenge, with most people gaining back most, if not all, the lost weight.2 This can lead to frustration and increase chances of not staying with an exercise program.  However, from a health perspective it must be emphasized that being physically active results in substantial health benefits independently of weight loss (see Table).  In other words, one can gain health benefits from exercise without necessarily losing weight.  In view of the fact that exercise alone rarely results in significant weight loss, especially in women,3 acknowledging the "weight loss-independent" health benefits of exercise is an important public health message.  Some of the many health benefits of exercise, independent of weight loss, are described below, with a summary table at the end.

Improvements in Glucose Metabolism and Insulin Action

Regardless of age and health status, regular exercise can lower fasting blood glucose and insulin,4,5 reduce glycated hemoglobin (HbA1c),4 and increase glucose tolerance6,7 and insulin sensitivity.4-13  These beneficial effects can occur after just one exercise session of moderate intensity, such as a 30-minute brisk walk.11,12  A vigorous bout of exercise, such as jogging for 30 minutes, can increase insulin sensitivity for up to 3 days.

Aerobic exercise and strength-training modes of exercise appear to be equally effective for improving glucose metabolism and insulin sensitivity.  Just last year it was reported that 3 days per week of either aerobic exercise (40-50 minutes at ~75-80% of maximum heart rate) or strength training (1-2 sets of several upper- and lower-body exercises) was sufficient to improve insulin sensitivity in sedentary, overweight and obese middle-aged men by 20% to 25%.13  Body weights remained essentially unchanged during the 6-month program, suggesting the decreases in body weight were not required for improving insulin sensitivity.

Even moderate-intensity physical activity provides benefits, sometimes equal to that of higher-intensity exercise.  In a study of overweight women and men at risk for cardiovascular disease, it was found that walking 10-11 miles per week (i.e., 3-4 walking sessions per week, ~40-60 minutes each) improved insulin sensitivity just as much as jogging 16-17 miles per week (i.e., 3-4 sessions per week, ~40-60 minutes each).10   This suggests that intensity is not nearly as important as the total amount of time actually spent exercising.  The jogging group lost a little more weight (~5 pounds), compared to the walking group (which lost less than 2 pounds over 8 months), mainly because they burned more calories by covering more distance during the exercise sessions.  However, both groups improved their insulin sensitivity by the same amount, suggesting that weight loss itself was probably not the key factor.

In addition to increasing insulin sensitivity, both aerobic and resistance exercise training can improve glycemic control.4  A thorough analysis of 27 exercise studies revealed that exercise training in patients with type 2 diabetes produced modest beneficial reduction in HbA1c of ~0.8%.4  The authors noted that this effect is similar to that observed with dietary, drug and insulin treatments.  Weight loss appeared to have little to do with the improvement in glycemic control.  For example, the improvement in HbA1c with aerobic exercise training alone (-0.7%) was about the same as that observed for combined aerobic and resistance exercise training (-0.8%), even though weight loss was greater for the combined training (a loss of 5.1% of initial body weight) than for aerobic exercise training alone (a loss of 1.5% of initial body weight). 

Blood Pressure

Exercise reduces blood pressures.12,14-17  Similar to insulin sensitivity, the blood pressure-lowering effect of exercise is observed after just one exercise session, and can last for hours.12  Exercise does not even have to be structured.  Accumulation of lifestyle physical activity throughout a single day significantly reduced ambulatory blood pressures in overweight prehypertensive and obese hypertensive men and women for 6 to 8 hours after the period of increased activity had ended.16   The blood pressure-lowering effect of the accumulated physical activity was greater in men and women who had the highest blood pressures to start.  For example, in prehypertensive adults, systolic blood pressure was ~6-7 mmHg lower during the first 6 hours after the period of increased lifestyle physical activity was completed, and in hypertensive adults the systolic blood pressure was ~12-13 mmHg lower for the first 8 hours after the period of increased lifestyle physical activity was completed.  It is worth noting that the researchers found no relationship between the reduction in blood pressure and how much physical activity was actually performed during the period in which the participants were asked to be more active.  This suggests that modest increases in physical activity are beneficial for reducing blood pressure in overweight individuals with elevated blood pressure.  In fact, moderate-intensity activity is just as effective as higher-intensity activity for lowering blood pressures.5,15,16

It also must be emphasized that reductions in blood pressure after exercise training do not appear to be related to decreases in body weight.15  A thorough examination of 72 exercise intervention trials found that training induced significant reductions in resting and ambulatory blood pressure among hypertensive individuals on the order of 5-7 mmHg.5  These improvements occurred despite minimal changes in body weight (~1.2 kg) and percent body fat (~1.4%).  In fact, decreases in body weight explained less than 1% of the changes in blood pressure with exercise training.15

Lipids and Lipoproteins

A single exercise session (e.g., 30 minutes of brisk walking) acutely lowers triglycerides and increases HDL-cholesterol (the good cholesterol).12,18  Changes in blood lipids after longer-term exercise training studies are less clear, but does appear that regular exercise, even in the absence of significant weight loss, can improve overall lipid and lipoprotein profiles.12, 18,19  Unlike insulin sensitivity and blood pressure, which can improved with very modest amounts of moderate-intensity exercise, improvements in lipids and lipoproteins may require a greater dosage of exercise.  For example regular exercise equivalent to jogging 17-18 miles/week improved 11 different lipid and lipoprotein variables significantly more than lower amounts of physical activity (equivalent to walking or jogging 11 miles/week).19  The authors emphasized that the widespread improvements in lipoprotein profile were achieved with little weight change.

That weight loss is not necessary for improvements in lipids and lipoproteins to occur is reinforced by a recent report showing that among both overweight nondiabetics and obese diabetics, 8 weeks of aerobic exercise significantly reduced total cholesterol and LDL-cholesterol (the bad kind), and increased the ratio of HDL-cholesterol to total cholesterol, but did not significantly alter body weight or fat mass. 8

Blood Vessel Health

Exercise improves blood vessel health.8,20,21  Among overweight and obese persons with and without diabetes, eight weeks of aerobic exercise training (40 minutes at a moderate-to-vigorous intensity, 4 times/week) significantly increased the capacity of the participants' arteries to dilate in response to increases in blood flow.8  The improvement in vascular dilatory function coincided with enhanced insulin sensitivity and increased aerobic capacity, but occurred in the absence of changes in body weight and total fat mass.

In addition to aerobic exercise, strength training has also been reported to improve vascular health.20,21  Among overweight women, after 1 year of resistance training (> two sessions per week; three sets of 8-10 repetitions, targeting all major muscle groups), arterial dilation in response to an increase in blood flow was increased 41% (whereas a matched control group actually demonstrated a worsening of arterial dilation capacity during the year-long study).21

Reduced Chances of Thrombosis (blood clot)

An additional benefit of exercise training for overweight/obese individuals, regardless of changes in body weight, is reduced risk of a major vascular thrombotic event (i.e. less chance of having a blood clot in a major artery).22  Acute moderate-intensity exercise appears to result in biochemical changes in the blood that reduce chances of having a blood clot (i.e., blood platelets are less likely to stick together), and it enhances enzymes responsible for dissolving chemicals that tend to form clots (i.e., moderate-intensity exercise can enhance fibrinolysis).22   The enhanced fibrinolytic response may be related to increases in t-PA.20,22  These anti-thrombotic adaptations appear to be largely independent of changes in body composition.

One particularly important enzyme, endothelial tissue-type plasminogen activator (t-PA), tends to be lower in overweight and obese persons, thus making them more susceptible to a major vascular thrombotic event.  It was recently shown, however, that a 3-month exercise program (40-50 minutes at 60-75% maximum heart rate, 5-7 days/week) increased t-PA release capacity in overweight and obese men and women to levels similar to that of non-overweight individuals.20   This significant improvement occurred in the absence of reductions in body weight or body fat. This suggests that the impaired endothelial t-PA release is more likely attributable to a sedentary lifestyle rather than overweight or obesity per se.

Inflammation

Inflammation may play a key role in chronic diseases such as cardiovascular disease and diabetes.  A number of inflammatory biomarkers in the blood have been reported to be reduced after aerobic exercise training.23-26  For example, it was recently reported that among overweight persons at risk of coronary events, 12 weeks of aerobic exercise training significantly reduced three key inflammatory biomarkers (IL-8,  monocyte chemoattractant protein-1, matrix metalloproteinase-9) that have been linked to cardiovascular disease.26  Body weight was not changed in this study.  Although the mechanisms for the anti-inflammatory effects of regular exercise are not well understood, the protective effect of regular physical activity may be due in large part to the anti-inflammatory response elicited by a single bout of exercise.24

Metabolism after a Meal

The postprandial period (i.e., ~1-6 hours after a meal) may be important in the development of cardiovascular disease.  Elevated blood fats during this period have been linked to impaired blood vessel health and atherosclerotic plaque formation.27,28  Acute exercise, as well as regular exercise training, have beneficial effects on reducing the degree to which blood fats are elevated after a meal.27,28    It was recently reported that in obese men, 60 minutes of exercise at a low-, moderate-, or vigorous-intensity, performed 12 hours before ingestion of a fat-rich meal, attenuated the increase in blood fats (tryglycerides) during an 8-hour postprandial period.28  It is important to note that the reduced postprandial blood fat response observed 12 hours after a single exercise session28 is similar to the reduction reported after 7 weeks of exercise training,29 suggesting that much of the apparent "blood fat lowering" effect of regular exercise may due to the last exercise bout.  The observation that low- and moderate-intensity exercise are just as effective as higher-intensity exercise may be particularly relevant for sedentary and minimally-active individuals.

Conclusions

Although weight loss is a desired outcome for many persons, it may be more prudent to focus on increasing physical activity rather than a specific weight loss goal.  Data from the Finnish Diabetes Prevention Study30 and the Diabetes Prevention Program in the United States31 indicated that up to twice as many participants were able to achieve the physical activity target (~150-210 minutes/week; or ~20-30 minutes per day) than were able to achieve the weight loss goal (>5-7% loss of initial body weight).  These studies suggest that it may be easier to improve "fitness" than it is to achieve "thinness."

From a public health perspective, it is essential to emphasize that women and men of all sizes and shapes can reap important health benefits from physical activity in the absence of weight loss (see Table).   Therefore, physically inactive individuals considered at increased risk for cardiovascular disease and diabetes due to both a sedentary lifestyle and a high body weight should be encouraged to engage in regular physical activity, regardless of whether a more active lifestyle leads to weight loss.

When it comes to exercise, body weight, and health benefits, it really is possible to gain without losing.

References

  1. American College of Sports Medicine:  Position Stand: Appropriate intervention strategies for weight loss and prevention of weight gain for adults.  Med Sci Sports Exerc 2001; 33: 2145-2156.
  2. Anderson JW, Konz EC, Frederich RC, Wood CL:  Long-term weight-loss maintenance: a meta-analysis of US studies.  Am J Clin Nutr 2001; 74: 579-584.
  3. Donnelly JE, Smith BK: Is exercise effective for weight loss with ad libitum diet? Energy balance, composition and gender differences. Exerc Sport Sci Rev 2005; 33: 169-174.
  4. Snowling NJ, Hopkins WG:  Effects of different modes of exercise training on glucose control and risk factors for complications in type 2 diabetic patients.  Diabetes Care 2006; 29: 2518-2527.
  5. Cornelissen VA, Fagard RH:  Effects of endurance training on blood pressure, blood pressure-regulating mechanisms, and cardiovascular risk factors.  Hypertension 2005; 46: 667-675.
  6. Bruce CR, Thrush AB, Mertz VA, et al. :  Endurance training in obese humans improves glucose tolerance and mitochondrial fatty acid oxidation and alters muscle lipid content.  Am J Physiol Endocrinol Metab 2006; 291: E99-E107.
  7. Kelley DE, Goodpaster BH:  Effects of physical activity on insulin action and glucose tolerance in obesity.  Med Sci Sports Exerc 1999; 31 (Suppl): S619-S623.
  8. De Fillipis E, Cusi K, Ocampo G, et al.:  Exercise-induced improvement in vasodilatory function accompanies increased insulin sensitivity in obesity and type 2 diabetes mellitas.  J Clin Endocrinol Metab 2006; 91-4903-4910.
  9. O'Donovan G, Kearny EM, Nevill AM, et al.:  The effects of 24-weeks of moderate- or high-intensity exercise on insulin resistance.  Eur J Appl Physiol 2005; 95: 522-528.
  10. Houmard JA, Tanner CJ, Slentz CA, et al.:  Effect of the volume and intensity of exercise training on insulin sensitivity.  J Appl Physiol 2004; 96: 101-106.
  11. Braun B, Zimmerman MB, Kretchmer N:  Effects of exercise intensity on insulin sensitivity in women with non-insulin-dependent diabetes mellitus.  J Appl Physiol 1995; 78: 300-306.
  12. Thompson PD, Crouse SF, Goodpaster B, et al.: The acute versus the chronic response to exercise.  Med Sci Sports Exerc 2001; 33 (Suppl): S438-S445.
  13. Ferrara CM, Goldberg AP, Ortmeyer HK, Ryan AS:  Effects of aerobic and resistive training on glucose disposal and skeletal muscle metabolism in older men.  J Gerontol 2006; 61A: 480-487.
  14. Pinto A, Di Raimondo D, Tuttolomondo A, et al.:  Twenty-four tour ambulatory blood pressure monitoring to evaluate effects on blood pressure of physical activity in hypertensive patients.  Clin J Sport Med 2006; 16: 238-243.
  15. Fagard RH:  Physical activity in the prevention and treatment of hypertension in the obese.  Med Sci Sports Exerc 1999; 31 (Suppl): S624-S630.
  16. Padilla J, Wallace JP, Park S:  Accumulation of physical activity reduces blood pressure in pre- and hypertension.  Med Sci Sports Exerc 2005; 37: 1264-1275.
  17. Kelley G:  Dynamic resistance exercise and resting blood pressure in adults: a meta-analysis.  J Appl Physiol 1997; 82: 1559-1565.
  18. Leon AS, Sanchez OA:  Response of blood lipids to exercise training alone or combined with dietary intervention.  Med Sci Sports Exerc 2001; 33 (Suppl): S502-S515.
  19. Kraus WE, Houmard JA, Duscha BD, et al.:  Effects of the amount and intensity of exercise on plasma lipoproteins.  N Engl J Med 2002; 347: 1483-1492.
  20. Van Guilder GP, Hoetzler GL, Smith DT, et al.:  Endothelial t-PA release is impaired in overweight and obese adults but can be improved with regular aerobic exercise.  Am J Physiol Endocrinol Metab 2005; 289:E807-E813.
  21. Olson TP, Dengal DR, Leon AS, Schmitz KH:  Moderate resistance training and vascular health in overweight women.  Med Sci Sports Exerc 2006; 38: 1558-1564.
  22. Wang J-S: Exercise prescription and thrombgenesis.  J Biomed Sci 2006; 13: 753-761.
  23. Woods JA, Viera VJ, Keylock KT:  Exercise, inflammation, and innate immunity.  Neurol Clin 2006; 24: 585-599.
  24. Petersen AMW, Pedersen BK:  The anti-inflammatory effect of exercise.  J Appl Physiol 2005; 98: 1154-1162.
  25. Kohut ML, McCann DA, Russell DW, et al.:  Aerobic exercise, but not flexibility/resistance exercise, reduces serum IL-8, CRP, and IL-6 independent of B-blockers, BMI, and psychosocial factors in older adults.  Brain Behavior Immunity 2006; 20: 201-209.
  26. Niessner A, Richter B, Penka M, et al.: Endurance training reduces circulating inflammatory markers in persons at risk of coronary events: impact on plaque stabilization? Atherosclerosis 2006, 186:160-165
  27. Pettit DS, Cureton KJ:  Effects of prior exercise on postprandial lipemia: a quantitative review.  Metabolism 2003; 52: 418-424.
  28. Zhang JQ, Ji LL, Fretwell VS, Nunez G:  Effect of exercise on postprandial lipemia in men with hypertriglyceridemia.  Eur J Appl Physiol 2006; 98: 575-582.
  29. Weintraub MS, Rosen Y, Otto R, et al. :  Physical exercise conditioning in the absence of weight loss reduces fasting and postprandial tryclyceride-rich lipoprotein levels.  Circulation 1989; 79: 1007-1014.
  30. Tuomilehto J, Lindstrom J, Eriksson JG, et al.:  Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance.  N Engl J Med 2001; 344: 1343-1350.
  31. Knowler WC, Barrett-Connor E, Fowler SE, et al.:  Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin.  N Engl J Med 2002; 346: 393-403.

 

Table.  Health benefits of physical activity, independent weight loss

Glucose metabolism and insulin action

Decreased fasting glucose 

Decreased fasting insulin        

Increased glucose tolerance   

Increased insulin sensitivity   

Decreased HbA1c                         

Blood Pressures

Decreased Systolic Blood Pressure    

Decreased Diastolic Blood Pressure    

Lipids and lipoproteins

Decreased LDL-cholesterol                   

Increased HDL-cholesterol                   

Decreased triglycerides                                   

Improved LDL and HDL Subfractions                

Blood Vessel Health

Increased vascular dilatory function     

Reduced Risk of Blood Clots

Increased t-PA release capacity           

Decreased platelet reactivity          

Enhanced fibrinolysis                         

Decreased plasminogen activator inhibitor-1  

Inflammation

Decreased proinflammatory markers                       

Postprandial metabolism

Attenuation of rise in blood fats after a meal                        

Reduced blood glucose response after a meal                        

HIC# 11143