HOW MUCH SHOULD I EXERCISE?

This isn't a question anyone can give a blunt answer to without knowing you personally, and what your goals in actively exercising are. Obviously somebody looking to become a mountain requires intense weight lifting, a modified diet and probably some cardio vascular work to improve muscle definition. If all you're looking to do is maintain your current image however, or maybe just lose a few pounds less commitment is required. Covering the broad spectrum of such cases is beyond the scope of this webpage, but providing information about maintaining a standard level of fitness (decreasing net energy balance) is the focus of this section.

Whoa now! Where did that whole "energy balance" thing come from? Energy balance deals with the concept of matching your eating habits to fit your level of exercise, or vice versa. Energy intake is the amount of energy you gain daily through what you eat, and energy expenditure is how much you use through the course of the day. Energy balance then, is the net energy left over or missing at the end of the day.

In a study conducted by Biomathematics and Statistics Scotland, variations in exercise level were monitored in volunteers, who were fed ad libitum (similar to a buffet, where the volunteers chose how much and when to eat). Results found that a decrease in physical activity corresponded to decrease energy expenditure and energy intake, but an increase in energy balance. The cases of low exercise levels lead to a significantly positive energy balance, most of which was stored by fat (Stubbs RJ, Hughes DA, Johnstone AM, Horgan GW, King N, Blundell JE).

The implications are that decreased levels of physical activity when there is no control over diet leads to a build up of excess energy in the form of fat. A person who practices two hours daily with their rowing team versus one who is so bogged down by homework that they can't leave their room have very different energy expenditures, and maintaining a similar diet will not result in similar fitness. You need to match your eating habits to your lifestyle. The rower requires a higher energy intake to maintain his/her energy levels throughout the day, whereas others may require significantly less.

Assuming you're an average university student then, just how much exercise is required to maintain a net energy balance close to zero? A study by CA Slentz et al. in January 2004 attempted to determine the amount of activity required to prevent weight gain by examining energy balance in overweight individuals aged 40-65 years. They found that in a sample of non-dieting individuals, control groups gained weight, while those in the low and higher exercise brackets lost weight.

"These findings strongly suggest that, absent changes in diet, a higher amount of activity is necessary for weight maintenance and that the positive caloric imbalance observed in the overweight controls is small and can be reversed by a modest amount of exercise. Most individuals can accomplish this by walking 30 minutes every day." (Slentz, CA et al)

The 30 minutes referred to are in addition to normal daily activities in the age group. Clearly the study was considering in the age bracket, which isn't quite the same as that of the average university student so a bit of discretion is necessary. Still, we can see how little it can take to maintain a negative energy balance. Going out for a short walk, or maybe just jogging between classes could be all it takes, depending on your energy intake.

So in general we see that fitting you exercise levels to your eating habits, and you're eating habits to your exercise levels is an important life skill. This doesn't just include what you eat, but when you eat. Eating right before you go to bed increases your energy intake, but your body is at rest and your metabolism doesn't expend all that energy you just fed your body, and most of it becomes stored as fat. Cutting down on carbohydrate intake around 4 hours before sleeping can minimize this effect. Similarly, eating breakfast at the start of the day provides energy to help support you throughout the day. Keeping a mind on energy intake and expenditure allows you to dictate how you want your body to change. You can loose weight, raise energy levels or simply maintain your current image. Once again, striking the balance as to what you consider healthy for yourself, is up to you.