Energy

• Energy is not a nutrient but is required in the human body for metabolic processes, physiological functions, heat production, muscular activity, growth and synthesis of new tissues.
  Energy is released from food components by oxidation.
• The main sources of energy are carbohydrates, proteins, fats and, to a lesser degree, alcohol.
• 1 kcal = 4.2 kJ
• 1 gram fat = 38 kJ or 9 kcal
• 1 gram carbohydrate = 17 kJ or 4 kcal
• 1 gram protein = 17 kJ or 4 kcal
• 1 gram alcohol = 29 kJ or 7 kcal
• Daily energy requirements vary with age, gender, body size and activity, recommendations are needed for each age and gender group.
• WHO has set daily energy requirements for men at 2500 kcal and for women at 2000 kcal.
• Daily energy requirements are 30-35 kcal per kg healthy body weight.
  A healthy body weight has a BMI of 18.5-25.
• Daily energy requirements can also be calculated by resting metabolic rate multiplies PAL-value.

• Daily energy requirements consists of three components:
  1. Basal metabolic rate (BMR)
  2. Diet-induced energy expenditure (DEE) and
  3. Activity-induced energy expenditure (AEE).
• Activity-induced energy expenditure accounts for 15-30% of daily energy requirements.
• Resting metabolic rate accounts for 60-75% of daily energy requirements.
• Resting metabolic rate (RMR) is basal metabolic rate + diet-induced energy expenditure.
• A high basal metabolic rate also gives a high resting metabolic rate because diet-induced energy expenditure is the same for both men and women.
• Basal metabolic rate (BMR) averages 5 to 10 percent lower in women than in men. This is largely because women generally possess more body fat and less muscle mass than men of similar size.
• Basal metabolic rate can be calculated as followed:
  1. 11 kcal for every 0.5 kg of body weight for women
  2. 12 kcal for every 0.5 kg of body weight for men
• Fat tissue has a lower metabolic activity than muscle tissue. As lean muscle mass increases, basal metabolic rate increases and therefore, also resting metabolic rate.
• Strength training can increase basal metabolic rate due to increasing the muscle tissues.
• It is easier to lose weight with a high basal metabolic rate.
• Resting metabolic rate for men is about 1600 kcal and for women about 1300 kcal. Resting metabolic rate should be maintained (preferred increased) when following a diet.
• Needed energy during physical exercises is derived from oxidation of carbohydrates, proteins and/or fat.
• Carbohydrate play a key role in the performance of exercise lasting 60-90 minutes.
• Primarily carbohydrates are used during the first several minutes of physical exercise.
• For an average fit person, it takes 20 to 30 minutes of continuous aerobic activity to burn 50% fat and 50% carbohydrate.
• Proteins contribute less than 2% of the energy sources used during exercise of less than 1 hour.
• During the final minutes of exercise lasting 3 to 5 hours, protein utilization may reach 5-15% of the fuel supply.
• Low intense exercise (30% VO2 max) relies primarily on fat whereas high intense exercise (>70% VO2 max) primarily utilized carbohydrate.
• Fat oxidation is dependent on carbohydrate oxidation.
• Total carbohydrate use is highest at 85% VO2max.
• Total fat oxidation is the highest at 65% VO2max.
• Lactic acid is removed more rapidly at 30-40% VO2max.
• Phosphocreatine (PCr) is a major source of muscular energy during short-term, high-intensity exercise bouts lasting from approximately 2 to 30 seconds.
• Exercise for 60 minutes at low intensity has no effect on the skeletal muscle carnitine pool.
• The hierarchy for substrate oxidation in humans:
  1. Alcohol has highest priority for oxidation because there is no body storage pool and conversion of alcohol to fat is energetically expensive.
  2. Amino acids are next in the oxidative hierarchy. Again, there is not a specific storage pool for amino acids. Body proteins are functional in nature and do not serve as a storage depot for amino acids.
  3. Carbohydrates are third in the oxidative hierarchy. There is a limited capacity to store carbohydrate as glycogen and conversion of carbohydrate to fat is energetically expensive.
     Carbohydrate is also somewhat unique in that it is an obligatory fuel for the central nervous system, brains and the formed blood elements (e.g. red blood cells).
  4. Proteins are fourth in the oxidative hierarchy.
  5. Fats are fifth in the oxidative hierarchy because in contrast to the other macronutrients there is a virtually unlimited storage capacity for fat.
     Because of the lowest priority for oxidation the body could not easily lose fat.

Scientific studies on the relationship between energy and disease prevention:
A review article of randomized, placebo-controlled double blind clinical trials (RCTs) will answer the following question:
"Do taking dietary supplements make sense?" Yes for a positive conclusion and no for a negative conclusion.

A review article of cohort studies or case-control studies will answer the following question:
"Should I change my diet?".

1. Aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state