Digestion & Diet Induced Thermogenesis

When protein reaches the stomach it stimulates the release of hydrochloric acid which starts the process of breaking down the polypeptide chain into shorter segments of amino acids. These amino acids (dipeptides and tripeptides) then travel to the small intestines where they are broken down again and absorb. Once absorbed they travel through the hepatic vein to the liver where they are processed into glucose or fat or released into the bloodstream. Tissues in the body use amino acids for glucose production, growth and maintenance and other vital cellular functions. Amino acids are the basic components of hormones, which are essential chemical signaling messengers of the body. (more protein info here)

About your liver
“Some functions of the liver are: to produce substances that break down fats, convert glucose to glycogen, produce urea (the main substance of urine), make certain amino acids (the building blocks of proteins), filter harmful substances from the blood (such as alcohol), storage of vitamins and minerals (vitamins A, D, K and B12) and maintain a proper level or glucose in the blood. The liver is also responsible for producing cholesterol. It produces about 80% of the cholesterol in your body.”

Carbohydrates are foods rich in sugar called saccharides. In order to be absorbed they need to be broken down into monosaccharides. The enzyme salivary amylase begins the digestion process in the mouth. Enzymes are used to break down polysaccharides (found in most carbs) into disaccharides and monosaccharides. Energy is released each time these bonds are broken. These polysaccharides pass through the stomach and into the duodenum where the pancreas releases pancreatic amylase further breaking down the polysaccharides into disaccharides. The disaccharides move into the small intestines where they are broken down by the brush border enzymes into monosaccharides. Once reduced to monosaccharides the liver then absorbs them to be used for energy.(a cool interactive video)

Some fat digestion takes place in the stomach but most of it takes place in the small intestines. When fat enters the small intestines the pancreas releases pancreatic lipase this substance splits dietary fat back into its component parts, glycerol and fatty acids. The liver then releases bile to work hand in hand with the lipase to aid in digestions. This is important because fat cannot be mixed with water or water soluble substances. An alteration must occur which is called emulsification where each droplet of fat is surrounded by a droplet of bile. The bile is used as an emulsification substance in order to hold the fat in solution long enough to be absorbed.

“The other important factor in bile is the bile salts. They are the chemicals that act in fat metabolism to emulsify dietary fats. The emulsified fat droplets present a lot of surface area for the action of the enzymes, which are water soluble. As a result, fat and fat-soluble vitamins are able to be absorbed through the walls of the small intestines. After the bile salts do their work, the liver reabsorbs them from the blood so that they can be used again.”

Now that we have talked about digestion lets talk about energy required to digest each nutrient. Diet Induced Thermogenesis or DIT for short. DIT is the energy used by the body to digest and absorb nutrients.

A more technical definition:
“Diet induced thermogenesis (DIT) can be defined as the increase in energy expenditure above basal fasting level divided by the energy content of the food ingested and is commonly expressed as a percentage. It is, with basal metabolic rate and activity induced thermogenesis, one of the three components of daily energy expenditure.”

DIT is said to account for approximately 10% of daily energy expenditure. When food is consumed the body temp is elevated in turn activating the nervous system to increase resting metabolic rate. The type of nutrient plays a big part in the amount of DIT. The DIT of each nutrient is approximately 25% for protein, 5% for carbohydrates and 2% for fat. What this means is that when consuming protein 25% of the calories digested goes to digesting and absorbing that nutrient. But don't get carried away here because DIT is also dependent upon amount of calories ingested at one time. (DIT further reading...)

As usual my main focus here is to eat protein. It helps you build muscle, stay healthy, lose weight and has a Diet Induced Thermogenesis of 25%. Protein is also more satiating than carbohydrates and fat in the long and short term.

Exercise induced growth hormone

Growth Hormone is made by the pituitary gland and is needed for growth. It plays an important role in how the body uses food for energy (metabolism). The amount of GH in the blood changes during the day and is affected by exercise, sleep, emotional stress, and diet.

Cortisol is consider catabolic the opposite of growth hormone which is anabolic. Cortisol mobilizes energy by tapping into the bodies fat stores. It then moves these fat stores from one location to another fueling hungry working muscles. Energy regulation and mobilization are two critical functions of cortisol. However, if there is too much cortisol in circulation, abdominal obesity can develop.

Research has shown that lactic acid increases the secretion of growth hormone.(study) By increasing your bodies lactic acid production you are helping your body stay young and lose weight due to increased growth hormone. So training for that lactic acid burn should be used often in your workouts when trying to lose weight. Interval type exercises with high reps and limited rest work best to quickly stimulate lactic acid and not overstimulate cortisol. Remember anything over 47 minutes doubles the effect of cortisol and could lead to not getting to sleep at night (if you workout in the evening).

Although cortisol isn't all bad you want to keep it at lower levels in the evening so growth hormone secretion can be elevated 2 to 3 hour into sleep. This will ensure a refreshed feeling in the morning. Cortisol levels are supposed to be naturally at their highest in the morning. Blood sugar levels are low at this time as well, this coupled with light running may allow your body to burn more fat. I say light running because your body will use free fatty acids as the primary source of fuel as long as you don't go over 65% of your VO2.

I have said before not to train on an empty stomach first thing in the morning because effects of cortisol are amplified. But the benefits of running, biking or rowing at low intensity far out weigh the negative effects of cortisol. This is the case as long as intensity is low, not to exceed 65% VO2. The reason behind this is because at 25% VO2 fat supplies 80% of the muscles fuel. As your percent VO2 used increases your body begins to use more glycogen for fuel since it requires less oxygen to be converted to energy. You don't want to call on glycogen stores at this time because your body is primed for lipolysis. So if you can find the time 20 to 30 minutes of light running, biking, swimming or rowing first thing in the morning will help get rid of unwanted fat.