Recent Study Reveals Women Burn More Fat Than Men
Yuri Elkaim, BPHE, CK, RHN
A recent fat loss study published in the Journal of Applied Physiology (2005) has shown that women burn more fat than men during exercise. The researchers studied the effects of an incremental treadmill test to fatigue on 300 male and female subjects of varying fitness levels. They wanted to determine whether the ability to burn fat was influenced by gender, training status, fat free mass (lean body mass), and most importantly exercise intensity.
It has been well established that the most important determinant of fat burning during exercise is in fact exercise intensity, whereby fatty acids comprise roughly 55% of total energy expenditure at low intensities but diminish as exercise intensity increases. Conversely, as exercise intensity increases so too does the contribution of carbohydrates to total energy expenditure.
The shifting of fat and carbohydrate contribution to energy expenditure is known as the “crossover effect” and occurs anywhere from 50-75% of maximum heart rate depending on gender, training status, and the study cited. This is the point (or intensity) at which carbohydrates take over as the predominant fuel source for exercise.
This graph shows the crossover effect from the current study.
The present study found several interesting findings that have also been confirmed by numerous other studies. Some of these findings include:
1. Relative to lean body mass, women burn more fat than men at all exercise intensities.
There are many mechanisms thought to be involved in the fat oxidation difference between men and women; brieﬂy, these include levels of circulating hormones and catecholamines (adrenaline), muscle ﬁber type proportion, adrenergic regulation of fatty acid mobilization, and activity of the fat burning enzyme hormone-sensitive lipase.
This graph shows the contribution of fat (grey) and carbohydrates (black) at different exercise intensities for men and women in this study.
2. Fat is a greater contributor to total energy expenditure at lower exercise intensities.
This goes back to the “crossover effect” that was mentioned above. However, there are several mechanisms that inhibit fat burning at higher sustained intensities including lactic acid accumulation and an increasingly acidic cellular environment.
3. Fitter individuals burn more fat
Both VO2 max (maximum aerobic capacity) and training status are signiﬁcant predictors of fat oxidation. This would imply that VO2 max and training status can increase fat oxidation by increasing fat free mass and also by increasing the capacity of the muscle to burn fat. It also has been firmly established in training studies that trained individuals utilize more fat at the same relative (higher absolute) exercise intensity than untrained individuals. Training has also been shown to be an effective means of increasing fat oxidation during exercise in obese men and women and that the intensity found to induce these changes was low (40% VO2 max – roughly 50% of max heart rate).
Take Home Message
Based on these findings it is clear that the fitter you are the better your chances of burning fat. As your body adapts to endurance training it becomes better at saving important carbohydrate reserves and instead utilizes unneeded fat. Therefore, get active on a daily basis to allow your body to become a fat burning machine. The second piece of advice I’d like to give is to you is this… WALK EVERY SINGLE DAY! Why?
Well, as this studies (and tons of other studies have shown) low intensity exercise uses fat as a major source of fuel. Therefore, at a minimum you need to make walking (a relatively low intensity activity) a fundamental aerobic activity in your daily life. At least 30 minutes per day should do the trick. Take your dog for a walk, walk with your loved one, walk to work or home or to the grocery store – just do it!
Reference: Venables, M. et al. (2005). Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. J Appl Physiol 98: 160 –167, 2005.
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