You are what you eat Flashcards
What is nutrition?
what is process broken down into? (6)
what is a better definition of nutrition?
Nutrition: “The sum of the processes concerned with growth, maintenance and repair of the living body as a whole, or its constituent parts”
This process is broken down into different stages:
- Ingestion
- Digestion
- Absorption
- Transport
- Assimilation
- Excretion
This definition overlooks the fact that there are foods that have non-nutritional value.
Therefore, a better definition would be nutrition is concerned with understanding the effects of food on the human body in health and disease
Diet, Food and Nutrients
define
- Diet: The sum of food consumed by a person
- Foods: Substances that we take into the body
- Nutrients: The components of food
Factors that influence our diet:
- Personal beliefs
- Physiological (e.g. age)
- Economic
- Education
- Food characteristics
- Advertised
Foods are classified into different groups based on the nutrients they contain, we have the eat-well plate which tells us the foods that make up our diet and what proportions they should be in.
1/3 starchy carb, 1/3 fruit and veg, Non-dairy sources of protein, food high in fat/sugar and dairy.
Nutrients
macro and micro nutrients
what are macro nutrients? what are they used for?
what are micro nutrients? use?
Nutrients, the components of food, are divided into macronutrients and micronutrients
Macronutrients include:
Fat, carbs, protein and alcohol
• These can be used for energy, structural materials e.g. membranes, teeth, bones and can be used for hormone/enzyme synthesis
• Most energy dense is fat (9kcal/g), then alcohol (7kcal/g), then protein and carbs/CHO (4kcal/g)
Micronutrients include:
Vitamins and trace minerals
• These are used as cofactors in metabolism (e.g. thiamin/B1 in CHO and AA catabolism)
Food groups complement each other to give a balance of nutrients e.g. rice and peas
Proteins and amino acids
how many aminos acids?
what is an essential amino acid?
what is a complete protein?
what is an incomplete protein?
how can vegeterians get their amino acids?
There are 20 amino acids and of these we have some essential amino acids (Leucine, Valine, Threonine, Methionine, Phenylalanine, Lysine).
Essential AAs cannot be made by the body and hence we must obtain them through our diet.
A complete protein is a food that contains adequate amounts of all the essential amino acids e.g. fish, chicken, eggs, cheese
-> An incomplete protein is deficient in one or more essential acids.
But vegetarians can still get all their amino acids by protein combining, this is where they eat complementary proteins, these are two or more incomplete protein sources that when combined provide adequate amounts of all the essential amino acids.
E.g. Rice is limited by its lysine content, beans are limited by methionine content, but mixed together they are complete
Food composition and how we process them affects the way foods are handled in the body. Food processing effects the palatability, digestibility and metabolic response
Blood Glucose Regulation
3 fates of glucose?
what does insulin tell liver and muscles to do? adipocytes and liver to do?
When we intake carbs, glucose will enter our blood. This glucose has three possible fates:
- Used as an energy source through glycolysis
- Can be stored as glycogen
- Converted and stored as fat.
When we eat the meal our blood level rises, and insulin is released from the pancreas. Insulin tells liver and muscle cells to convert glucose to glycogen, it also tells them to convert amino acids -> protein and tells adipocytes/liver to convert glycerol -> FA to TAGs.
Blood Glucose Regulation
Insulin resistance
what does this mean?
what can this damage?
what is part due to insulin resistance?
Obese people can develop insulin resistance, so they must release more insulin to control their blood levels.
-> Type 2 DM is in part due to insulin resistance (so linked to obesity).
Insulin resistance means that cells do not absorb glucose from the blood stream, so blood sugar levels rise. This damages small and large blood levels leading to complications of diabetes -> retinopathy, heart disease, nephropathy, neuropathy,
Reducing the rate of glucose absorption into the blood therefore is useful for managing type 2-DM.
Glycaemic Index and how is it worked out?
what does this refer to?
how do you measure it?
Glycaemic index refers to the how much and how quickly a food will push your blood sugar levels up (rate and extent of rise in glucose after food).
You give person in fasting state 50g of glucose to eat and then measure their blood glucose levels (every 15min) over the next two hours.
You then send them away, put them back into fasting state, the next day you give them baked beans (for example, of testing GI of baked beans) to eat which contain 50g of available carbohydrate. You measure blood sugar over next 2 hours again and plot it.
The ratio of the area under that curve compared to the glucose one is the GI
What affects GI? Does a new potato or white bread have a lower GI?
what 2 things does the new potato have that lower GI?
what could increease or drecrease the GI? (4)
The new potato has a lower GI because the potato has more fibre which slows gastric emptying meaning everything enters the small bowel more slowly.
The new potato also has intact cell walls, cell walls inhibit access by digestive enzymes and slow digestion.
o If we added fat/protein this would further slow gastric emptying and digestion.
o If we peel the potato we increase the GI because we reduce the fibre content
o If we mash it we increase as broken cell wall
o If we add butter, we decrease as adding fat to delay stomach emptying
So, should we suggest type-2 diabetics to add butter to their meals?
NO! Because fat is our most energy dense macronutrient and type-2DM is (in part) caused by insulin resistance the main cause of which is being overweight/obese.
Why do we develop deficiency?
We need a balance of nutrients to stay healthy, if we do not get enough of one nutrient we will develop a deficiency disease.
Examples include: Kwashiorkor, rickets,
- Inadequate intake e.g. Reduced appetite, poor availability of food, vegetarian
- Reduced absorption e.g. Coeliac disease
- Increased losses e.g. diarrhoea, vomiting
- Increased demand e.g. growth, pregnancy
-> If demand outweighs supply of nutrients you will go through several stages of deficiency: health, subclinical deficiency, deficiency, death
Example: Vitamin A Deficiency
Vitamin A is stored and can last a long time, if you eat too much it can cause toxicity.
If you have a deficiency, first your liver stores become depleted, then your blood levels start to fall. At this point you become at increased risk of infection.
If the deficiency persists you can then develop Xeropthalmia, starting with night blindness which can progress onto complete blindness.
Estimating Nutritional Requirements
Vitamin c example
We can estimate nutritional requirements by looking at it in order to prevent/cure deficiency and toxicity (called minimal requirement) and/or we can estimate the level to optimise biochemical processes that rely on that nutrient.
E.g. Vitamin C
o 10mg/day avoids scurvy
o 20mg/day normal wound healing
o 30mg/day reduces risk of gingivitis
So 10mg/day is suboptimal! Therefore, this method is slightly flawed, as original minimal requirement isn’t good.
So rather than looking at the minimum to prevent deficiency/disease we could look at how much you need to maintain a balance between how much you take in and how much you use? Why is this flawed?
But this method is also flawed as our body adapts to our intake.
In experiments we found as our body pool of vitamin C for example decreased, the turnover of that nutrient decreased.
If a nutrient is in short supply, we can reduce the rate of turnover and/or increase absorption.
Why is excess iron bad?
50% of iron is carried in RBC as haemoglobin, its job being to carry oxygen. Excess iron generates free radicals -> this is damaging to cells however there are no excretory pathways for iron.
There are some losses via shedding cells (e.g. urinary tract, GI tract, skin, hair, bleeding). Therefore, we must be able to regulate iron absorption then store it and release according to demand.
How is iron transported and absorbed?
When iron is in our gut enterocytes, it enters the circulation by binding to transferrin. The iron-transferrin complex moves from the circulation to a new cell via the transferrin receptor. Most cells express these.
Once iron-transferrin complex binds to its receptor it enters via receptor-mediated endocytosis.
There is a drop of pH and this stimulates release of iron from transferrin. So, in order to alter iron absorption, we alter how many receptors we have on the cell surface, production of the iron-transferrin receptors is controlled by an iron regulatory protein.
