Meeting Energy Needs

from ACSM's Resources for the Personal Trainer 3rd Edition

Meeting Energy Needs for Optimal Weight and Body Composition

The relationship between weight and caloric intake is relatively simple:  If you eat more calories than you burn (expend), you will store the excess calories, and body weight will increase.  If you eat fewer calories than you burn, you will use some of your existing body tissues for needed energy, and body weight will drop.  Consistently consuming too little energy will burn enough of your lean mass (muscles) that the rate at which you burn calories (called the "metabolic rate") will decrease.  The end result of a lower metabolic rate is usually higher body weight (from more body fat) because you lose your ability to burn the calories you eat.  Therefore, staying in an energy-balanced state or deviating from it only slightly is an important strategy for both body weight and body composition maintenance. 

However, what happens during the day to achieve a state of energy balance makes a difference.  If you spend most of the day in an energy-deficit state (i.e., you burned far more calories than you consumed) but then eat a huge meal at the end of the day to satisfy your energy needs, you might still be in energy balance at the end of the day.  However, it appears that people who do this have different outcomes than those who maintain an energy-balanced state throughout the day.  Eating small but frequent meals has the following benefits:

• Maintenance of metabolic rate
• Lower body fat and lower weight on higher caloric intakes
• Better glucose tolerance and lower insulin response (making it less likely that fats will be produced from the foods you eat)
• Lower stress hormone production
• Better maintenance of muscle mass
• Improved physical performance

Surveys have suggested that people (particularly athletes) tend to delay eating until the end of the day, and many experience severe energy deficits earlier in the day (particularly on days when they train hard and need the energy the most!).  Problems with energy deficits include:

• Difficulty maintaining carbohydrate stores (this would impede endurance in high-intensity activities)
• Problems maintaining lean (muscle) mass
• Lower metabolic rate
• Difficulty meeting nutrient needs (foods carry both energy and other nutrients)
• Increased risk of injury (undernourished athletes may develop mental and muscular fatigue that, in some sports, would predispose them to injury)
• Missed opportunities to aid muscle recovery

Maintaining energy balance throughout the day by consuming small but frequent meals during the day is an excellent strategy for reducing these problems.