Energy Balance
When Energy Intake equals Energy Expenditure, the state of energy balance will be achieved, meaning your bodyweight will remain the same. Therefore, to lose weight, you need to eat less than your energy expenditure and conversely, to gain weight, you need to eat more than your body is expending.
The number of calories we burn in a day, otherwise known as Total Daily Energy Expenditure (TDEE), is highly dependent on three main factors that will be detailed below and visually depicted in the funnel diagram.
Main takeaways:
· BMR accounts for 60-80% of Total Daily Energy Expenditure- this is approximately 1kcal /kg / hour for males (0.9 kcal /kg for female).
· DEE accounts for ~10% for those followed a mixed diet.
· PAL contributes ~ 20-30% to TDEE although is the most variable contributing factor.
Total daily energy intake (TDEE) is composed of the energy costs of the processes essential for life at rest; known as basal metabolic rate (BMR), which contributes 60–80% of TDEE (Westerterp, 2013; Ravussin, Bogardus, 1989).
Dietary-induced energy expenditure (DEE)); is assumed to be 10% in subjects consuming the average mixed diet and implies the ‘energy spend’ of digesting foods, with protein requiring the most energy to digest which therefore is the macronutrient with the highest TEF (thermic effect of food).
Physical activity Level (PAL) appears to be the most variable cofactor in TDEE (Gerrior, Juan, Peter, 2006) and is of major importance to achieving energy balance. PAL depends on how active an individual is over a day but it usually accounts for approximately 20% to 30% of energy expended (Keim, Blanton, and Kretsch, 2004; Jakicic, 2002; Trumbo, Schlicker, Yates, and Poos, 2002) . The PAL for “sustained lifestyles” ranges between 1.1 – 1.2 and 2.0 – 2.5 for active lifestyles (Black, Coward, Cole and Prentice, 1996) whilst professional endurance athletes may reach PAL values around 4.0 (Westerterp, 2013) but it depends on the person and the activity. PAL variation can occur despite the same activity being carried out due to differences in bodymass, as modern man has a similar PAL as a wild mammal of a similar body size (Westerterp, 2013). However other energetic costs such as fat-free mass may be attributable to the reason why males appear to have a higher energy demand than women per kilogram of mass; as fat-free mass is the best independent predictor of BMR (Cunningham, 1991) as differences in resting muscle metabolism account for the majority of variance in metabolic rate among individuals (Zurlo, Larson, Bogardus & Ravussin, 1990).
In summary; PAL is the most variable factor that contributes to your daily energy expenditure that you can change RIGHT NOW, but your fat free mass (lean muscle) is the ultimate determinant of your basal metabolic rate (how many calories you burn at rest).