Nutritional aspects of food – food hypersensitivity and allergies
Allergy – via immune system (total avoidance) > immune system comes in contact with allergen and body
responds with immune response resulting in antibody production (Immunoglobuline E) and release of histamine
Intolerance – enzyme deficiency (small amounts tolerated)
Allergen – a protein:
- (partially) resistant to digestion
- Comes in contact with the immune system
- Is seen as ‘foreign’ to the immune system
- Present in foods in rather high concentrations
- Is regularly consumed
Symptoms food allergy in skin, respiratory tract and GI tract (most common: swelling, sneezing, nausea)
Anafylactic shock – very severe and even life threatening allergic reaction
5 types of antibodies produced by B-lymfocytes: IgG, IgA, IgM, IgE (mainly in bodily fluids and skin, associated
with allergic reactions) and IgD
An allergic reaction occurs through binding of 2 IgE molecules with the allergen. The binding sides of the allergen
are called epitopes. Thus, also 2 epitopes are necessary for an allergic reaction.
Linear epitopes – close to each other in the amino acid sequence (break it down by adding enzymes or
hydrolysis)
Conformational epitopes – close to each other because of the folded structure of the protein (heating so an
allergic person can still eat a certain food product)
Occurrence of an allergy: uptake of proteins
1. Sensitisation (1st contact: body comes into contact with allergen, breaks it down and makes antibodies
that are put on so-called mast cells)
2. Challenge (2nd contact: contact with the allergen and the mast cell that contains the antibodies causes
the mast cells to release histamine, which causes the symptoms of an allergic reactions)
Cause of differences between people with allergies: genetic and exogenous factors
Cross reactivity – higher chances that a certain allergies come hand in hand with another allergy
Histamine is also found in certain food products, such as fermented foods, fish and vegetables (low
concentrations). Effects can be higher blood pressure and headache, caused by an insufficient amount of
enzymes to break down histamine
Celiac disease – auto-immune disease not allergy or intolerance, no IgE’s involved, but IgA and IgG antibodies.
Immune system is activated by gluten in food and antibodies harm the intestinal wall and its villi. Destroyed villi
cannot absorb effective nutrients, resulting in lower uptake of fats, proteins, vitamins and minerals.
Gluten allergy – triggers an IgE antibody response.
4 kinds of proteins in wheat: albumines, globulines, gliadines and glutenines
Gluten = gliadines + glutenines
Nutritional aspects of food – lipid metabolism
Main source of fat in the diet: triacylglycerols, which are broken down in de duodenum by pancreatic lipases
into monoacylglycerols and fatty acids. 95% is absorbed in the small intestine (jejunum).
,Fatty acids can differ in:
- Chain length
- Degree of saturation (saturated, monounsaturated, polyunsaturated)
- Point of saturation (location of the double bond)
8 Most common fatty acids in our diet:
Saturated:
- Palmitic acid C16:0
- Stearic acid C18:0
Mono unsaturated:
- Oleic acid C18:1 (olive oil)
Poly-unsaturated:
- Linoleic acid C18:2 (sunflower oil)
- Linolenic acid C18:3 (linseed oil)
- Arachidonic acid C20:4
- Ecosapentanoic acid C20:5
- Docosahexanoic acid C22:6
The more solid a kind of fat at room temperature, the more saturated it is.
Fat absorption: pancreatic lipase breaks down the triacyclglycerols into fatty acids > villi in the small intestine
absorb the fatty acids > intestinal cells take up the fatty acids and remake the triglycerides (reesterification),
now called chylomicrons > which are taken up by the lymphatic system (this whole process takes about 1,5
hours)
Chylomicron:
Lipoproteins:
- Chylomicrons (large)
- VLDL = very-low-density lipoproteins
- LDL = low-density lipoproteins
- HDL = high-density lipoproteins (small)
Metabolism of chylomicrons: Chylomicrons are broken down by lipase in the capillary blood vessels > fatty acids
are then taken up by the tissue cells, and used for storage, as energy source (ATP) or signalling.
Roles of Adipose Tissue (fat tissue):
- Heat insulation
- Mechanical cushion
- Energy storage
- Endocrine function (producing hormones)
Fed state – muscle cells take up fat in the form of monoglycerides and fat tissue takes up fat in the form of
triglyceride
, Fasted state – fat tissue releases fat in the form of monoglycerides in the capillary blood vessels and are then
taken up by muscle cells.
Fatty acids taken up by cells and broken down through beta-oxidation in the mitochondria > fatty acid (acyl-CoA
(C18)) is turned into acetyl-CoA (C2) + fatty acyl-CoA (C16) > this fatty acyl-CoA (C16) is broken down again until
9 acetyl-CoA (C2) are formed.
Atherosclerosis – Fatty deposits collect on the inside of the arteries, which gradually narrow. This is mainly
caused by high levels of LDL.
Cholesterol levels in blood:
< 5.0 mmol/L = normal level
5.0-6.4 mmol/L = somewhat increased
6.4-7.9 mmol/L = increased
> 7.9 mmol/L = increased a lot
Trans fat (double bond in the trans configuration) – not bended fatty acid (produced during industrial processing
of fats, called hydrogenation, which protects the fat against oxidation and makes it more solid), naturally
present in milk and body fat of ruminants and present after processing in baked goods and margarine.
Cis fat (double bond in the cis configuration) – bended fatty acid, present in many vegetable oils
Sitosterol (plant sterol) present in special kinds of margarine lowers serum cholesterol.
Fat is often substituted by certain ingredients that cause a mouth feel similar to fat. An example of such an
ingredient is olestra (sucrose polyester, not absorbed, side effects such as diarrhea, affects absorption of lipid-
soluble vitamins (A, D, E, K), approved for snacks in the USA but not in the EU)
Nutritional aspects of food – fuel utilization in humans
Fuel requirements of tissues:
Brain – glucose
Skeletal muscle – fatty acids (resting), glucose (exertion)
Heart muscle – fatty acids
Adipose tissue – fatty acids
Liver – amino acids, fatty acids, glucose
