Does the cold weather make it harder to get in shape?

Now that winter is well and truly here (in England, at least), I've had a few questions from people wanting to know whether the cold weather makes it harder to get in shape.

I think it does.

This depends, of course, on where you live. What you're about to read assumes that it gets colder and darker in the winter, and lighter and hotter in the summer.

You see, there's plenty of research to show that your body will respond very differently to the same program of diet and exercise in the summer than it does in the winter.

Here's why...

Firstly, the temperature in which you exercise affects the number of fat calories your body burns for energy. Some evidence for this comes from a trial published in the journal Medicine and Science in Sports and Exercise [5]. Nine male subjects cycled for 90 minutes in several different temperatures.

• Minus 10 degrees Celsius

• 0 degrees Celsius

• 10 degrees Celsius

• 20 degrees Celsius

The number of fat calories burned for energy was reduced at both minus 10 degrees Celsius (0.15 grams of fat per minute) compared with 10 degrees Celsius (0.35 grams of fat per minute) and 20 degrees Celsius (0.40 grams of fat per minute). Previous research at Kent State University also shows an increase in protein breakdown when you exercise in the cold [1].

This is not the only study to look at the effect of cold air on fat metabolism. And the results are far from conclusive. In fact, during submaximal exercise in the cold, fat metabolism has been reported to be elevated, unchanged or reduced.

Other studies have combined whole body precooling before the exercise. This can reduce core body temperature, leading to a "shivering" response. It might explain why some trials show that the cold actually increases the amount of fat burned for energy.

In this study, the normal rise in core temperature associated with exercise stopped the subjects from shivering. That's why I think it's more relevant to people like you and me who exercise regularly.

Skin temperature also affects growth hormone levels. In fact, simply taking a hot (38-39 degrees Celsius) bath for 25 minutes will raise growth hormone levels more than ten-fold [4].

A single surge in growth hormone increases both the number of fat calories your body burns for energy and your metabolic rate [3]. That's why growth hormone therapy often leads to a reduction in fat mass (but it doesn't mean you can lose fat sitting in the bath — sorry).

Hibernation

Hibernating animals (those that sleep during the winter) tend to store fat before they hibernate. One of the ways they accomplish this is via an increase in the activity of enzymes (such as lipoprotein lipase, known also as LPL) that promote the storage of fat.

More interesting still, LPL levels in humans also rise and fall in tandem with the seasons [2]. Researchers from the University of Colorado studied a group of 12 women and 6 men in both the summer and winter.

Summer was classed as May through August. Winter was classed as November through February. LPL activity in both muscle and fat increased during the winter, and dropped during the summer.

Winter also sees a change in the activity of several fat-burning and muscle-building hormones.

For example, cortisol levels reach a low point in the summer [7]. Not only is cortisol associated with the storage of abdominal fat, it's also been linked to all kinds of health problems, including diabetes, heart disease and depression. Cortisol may also weaken your immune system, leaving you more susceptible to colds and flu.

Testosterone, a powerful hormone which helps you build muscle and lose fat, tends to peak in the summer and early autumn. It also reaches a low point in the winter and early spring [6].

Serotonin

There's also evidence to show that you'll find it harder to control your appetite in the winter rather than the summer. Some studies, for instance, show a link between the "winter blues" and a drop in serotonin levels [7].

Serotonin is a chemical that helps messages pass from one nerve cell to another. It helps different parts of your brain "talk" to each other.

When serotonin drops below a certain level, your brain "thinks" that your body is starving and "tells" you to start eating. In fact, some researchers believe that there's direct link between obesity (due to overeating) and decreased brain serotonin levels.

Overweight people with low levels of serotonin feel almost compelled to eat more. Once they get their carbohydrate "fix", serotonin levels rise, and they feel better again — albeit temporarily.

Dr Albert Stunkard, a professor of psychiatry at the University of Pennsylvania, thinks that people with an almost uncontrollable urge to raid the fridge late at night are doing it to help themselves sleep by boosting serotonin levels.

In other words, some people who suffer from the "winter blues" may use foods high in carbohydrate to make themselves feel better.

The bottom line is that many people will find it harder to get in shape in the winter rather than the summer. This is normal. During the winter months, it's perfectly reasonable to expect a slower rate of fat loss and muscle gain.

More information on how to gain muscle is available here (The Maximum Muscle Plan). And if you want to lose fat without losing muscle, this highly effective program (How to fight fat and win) works well for almost everyone who tries it.

References
1. Dolny, D.G., & Lemon, P.W. (1988). Effect of ambient temperature on protein breakdown during prolonged exercise. Journal of Applied Physiology, 64, 550-555
2. Donahoo, W.T., Jensen, D.R., Shepard, T.Y., & Eckel, R.H. (2000). Seasonal variation in lipoprotein lipase and plasma lipids in physically active, normal weight humans. Journal of Clinical Endocrinology and Metabolism, 85, 3065-3068
3. Gravholt, C.H., Schmitz, O., Simonsen, L., Bulow, J., Christiansen, J.S., & Moller, N. (1999). Effects of a physiological GH pulse on interstitial glycerol in abdominal and femoral adipose tissue. American Journal of Physiology, E277, 848-854
4. Koska, J., Rovensky, J., Zimanova, T., & Vigas, M. (2003). Growth hormone and prolactin responses during partial and whole body warm-water immersions. Acta Physiologica Scandinavica, 178, 19-23
5. Layden, J.D., Patterson, M.J., & Nimmo, M.A. (2002). Effects of reduced ambient temperature on fat utilization during submaximal exercise. Medicine and Science in Sports and Exercise, 34, 774-779
6. Smals, A.G., Kloppenborg, P.W., & Benraad, T.J. (1976). Circannual cycle in plasma testosterone levels in man. Journal of Clinical Endocrinology and Metabolism, 42, 979-982
7. Walker, B.R., Best, R., Noon, J.P., Watt, G.C., & Webb, D.J. (1997). Seasonal variation in glucocorticoid activity in healthy men. Journal of Clinical Endocrinology and Metabolism, 82, 4015-4019
8. Wurtman, R.J., & Wurtman, J.J. (1995). Brain serotonin, carbohydrate-craving, obesity and depression. Obesity Research, 3, 477S-480S