The Physiology of Hunger

Hunger is a powerful motivator

Your body is not a perfect calories burning machine – it is not as simple as energy in and energy out

You body is doing things exactly right thing.  What I need to do is to explain why.  Once you understand what is happening in your body you can learn to manage hunger and get rid of the cravings.

The body monitors the quantities of the various nutrients in our body.  We are motivated to eat when these stores fall below a critical level – it is self regulating.

There is a complex chemistry between body chemistry and emotions.  Hunger is not something to be got rid of. It is the results of:-

• Low nutrients in your body, especially glucose in the blood or tissues
• This causes metabolic signals and brain chemicals to be released
• These chemicals generate hunger for carbohydrates and proteins (also fats if fats are unbalanced)

Hunger is regulated in the body by sensors in the mouth, throat, liver, stomach and duodenum.  It is also regulated by chemicals that act on the brain and hypothalamus.  Eating is terminated by satiety receptors detecting sufficient food has entered the system.  These systems are switched on before nutrients are absorbed to stop us overeating.  The termination of feeding is handled by different systems than that responsible for the initiation of feeding. 

There are 3 main nutrients required by the body to function

1. Carbohydrates – which the body breaks down into glucose
2. Fats
3. Proteins – made up of amino acids

These are used by the body in different ways. 

Carbohydrate / Glucose Physiology

• Carbohydrates provide immediate fuel for the body
• There are fast carbohydrates and slow carbohydrates depending on how quickly and easily the body can break it down into glucose
• The brain demands glucose for energy
• The brain uses one third of all glucose in our body and it will maintain glucose levels at all costs
• The brain has sensors in the hypothalamus which detects a reduction in glucose
• The level of glucose is determined by insulin which is produced by the pancreas when a carbohydrate is eaten
• Insulin transports glucose to the cells where, in the presence of chromium and oxygen, it is burnt to produce heat

When glucose is too low either

The liver releases its stored glucose in to the blood (caused when adrenalin is released prompted by low glucose)
We search for food

• Overeating / binge eating means an excess of glucose is in the blood system which prompts the pancreas to produce excess insulin to cope.
• Excess insulin causes blood sugar levels to crash which causes abnormal cravings
• Also receptors, in response to too much insulin, reduce their sensitivity to insulin so more insulin is needed to ensure the same take up of glucose by the cells.
• All this leads to blood sugar instability which causes cravings, tiredness, irritability
• In effect the cells will be starved of glucose even though the person is well fed.
• Glucose that is not absorbed (due to the cells becoming resistant or overeating) is transported into fat cells by the insulin for storage.  In effect the body becomes a fat making machine not a fat burning machine
• Some glucose is also stored in the liver as glycogen
• If the brain is continually deprived the hypothalamus increases the set weight to encourage more eating

 
Fats

• Fat is converted into fatty acids in the liver and used for storage and making hormones
• We all have fats cells which expand as we eat more fat and store it and reduce as the fat is depleted
• As the fat cells expand they produce Leptin which switches of a NPY (Neuro Peptide y).  NPY stimulates hunger so switching it off means it switches off hunger pains.  This will continue until the fat cells return to ‘normal’ levels even if the person is having sufficient calories
• Similarly if fat calls are above ‘normal’ size eating behaviour is reduced
• Those who yo-yo diet find that their body does not respond to Leptin so NPY does not get switched off
• Fat is not immediately broken down into glucose for energy needs.  It is only used if glucose stores are depleted.
• A decline in fat storage triggers hunger.  Thus as you lose weight you get hungry
• Between meals the stored fat is converted into free fatty acids and provides a major source of energy (via Ketosis)
• Lack of fatty deposits results in lack of energy
• The hypothalamus detects a decrease in fat cells
• Glycerol is produced during the conversion of fats to free fatty acids.  A high level of glycerol in the brain triggers eating
   

Proteins (Amino Acids)

• Rich brain sensors monitor the levels of amino acids in the system.  These sensors stimulate hunger if amino acids are absent
• Protein is only used for energy on a reserve basis only
• Protein is held in a pool and used for tissue repair, immune system, water balance control, thyroid production, vision, bones and teeth