 
Of fitness and a Full Plate Q & A
Fall 2004 Series - Diabetes: diagnosis, management and emerging treatments
Q: Does the type of fat we eat (for instance high in PUFA) influence fat of the cell membrane (permeability, composition, whatever...)?
Response from Dr. Sheila Innis
A: Cell membranes are bilayers of fatty acids in molecules called phospholipids that make up the structure of cell membranes. The type of fat in the diet, as asked in this question, does have a marked effect on the composition of fatty acids in cell membranes throughout the body, and this includes the saturated and monounsaturated fats, as well as the amount and types of polyunsaturated fats.
In addition to influencing the properties of the membrane, such as the membrane permeability and how membrane enzymes, transport proteins and ion channels work, the membrane fatty acids are also a reservoir of fatty acids that are precursors for eicosanoids and other signal molecules. There has been considerable scientific interest in the ability of long chain omega 3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) which are particularly high in fish and fish oils to replace the n-6 polyunsaturated fats in cell membranes and in so doing to reduce the severity of some immune disorders, reduce plasma triglycerides, platelet aggregation and decrease the threshold for malignant arrhythmia. Other types of research have also suggested that higher amounts of n-3 fatty acids in the diet, and thus in cell membranes may improve insulin sensitivity in skeletal muscle.
Another important aspect of fatty acids is that they also regulate the expression of genes for key proteins involved in the regulation of carbohydrate and fat metabolism through receptors known as PPARs. These receptors are present in liver, muscle and adipose and heart and play a key role in how we regulate energy flux and fat storage.
Although much has yet to be learnt, the scientific evidence at this time favors a benefit of including a good source of the omega 3 fatty acids EPA and DHA from fish, or the precursor alpha linolenic acid from oils such as liquid canola oil or unhydrogenated margarine made with canola oil, flax seed oil, or walnuts, and reducing the amount of n-6 fatty acids in the diet.
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Q: Once a person has abdominal fat (large stomach and waist), if they lose weight and reduce the outside measurements, does this reduce the fat inside the stomach (intraabdominal)?
Response from Dr. Scott Lear
A: Yes, weight (being fat) loss regardless of whether it is the result of diet, exercise or medications (or any combination thereof) will result in decreases in intra-abdominal fat. At present there is no known weight loss regimen that will result in targeted fat reduction at a specific site. If as a result of a weight loss regimen, an individual looses centimetres/inches around their waist, it is quite likely that the amount of intra-abdominal fat will be reduced. This can sometimes be reflected in improvments to risk factors such as blood pressure, cholesterol and blood glucose.
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Q: Does everyone have significantly different metabolic rate?
Response from Dr. Scott Lear
A: Just like other physical characteristics (such as height, hair colour), metabolic rates will vary among randomly selected individuals. Among healthy individuals, resting metabolic rate can vary by 5%. Immediately following a bout of exercise, metabolic rate increases slightly and can stay slightly elevated for up to 24 hours. Several studies have investigated whether metabolic rate increases over the long-term as a result of regular exercise. Some of these studies indicate it can, while others show no difference. However, with regular exercise, you will be increasing your daily energy expenditure and thus burning more calories.
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Q: We heat up oils when we cook food - sometimes excessively - does this affect the composition of the oil and does this affect how the oils behave in our bodies? How so?
Response from Dr. Sheila Innis
A: Unsaturated vegetable oils contain carbon atoms that are not fully saturated with hydrogen atoms (thus the term unsaturated). In nature, unsaturated fatty acids are present in a configuration known as “ cis ” in which the hydrogen atoms present at a carbon-carbon double bond are located on the same side of the bond. This creates kinks and bends in the fatty acid chain and gives it fluidity. When oils with unsaturated cis double bonds are heated in the presence of oxygen the cis bonds can be altered, either by addition of hydrogen which would create a saturated fat, or by altering the hydrogen atoms so that they are on opposite sides of the double bond. When the hydrogen atoms are on opposite sides of the double bond, the fatty acid is known as a “trans” fatty acid. Trans fatty acids have straighter chains and higher melting points than cis unsaturated fats. The best evidence for an adverse effect of trans fatty acids on health is in the area of cardiovascular disease. Trans fatty acids raise LDL (bad) cholesterol and lower HDL (good) cholesterol; they also raise triglycerides and small dense LDL which are independently associated with increased risk of cardiovascular disease. The effects of trans fatty acids in increasing risk of cardiovascular disease has been estimated to be some where between 3 and 25 times higher than the risk associated with dietary saturated fats. Other areas of health concern for trans fats are in increasing the risk of type 2 diabetes, some immune and allergic disorders, and in adversely affecting fetal and infant growth. The evidence in these areas is inconsistent and insufficient to allow any conclusions to be made. In January 2004, Canada became the first country in the world to introduce mandatory labeling of trans fatty acids in the Nutrition Facts panel on foods, and you will see these new labels that state the amount of trans fats in foods start to appear on food packages. To avoid production of trans fats when preparing foods at home, do not use an oil for frying more than once and do not allow the oil to reach high temperatures. If you need to seal food in frying, once the food has been added to the pan with hot oil, quickly sear the food on all sides and reduce the temperature.
The picture below shows the major cis monounsaturated fat in nature, known as oleic acid, and its trans isomer called elaidic acid. Both fatty acids have the same molecular weight, with the same number of carbon and hydrogen atoms. The only difference is how the fatty acids are placed around the carbon double bond. Note how this changes the shape oft the fatty acid chain. This changes how they function in the body.
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