Vegetable oils in the modern diet
Vegetable oils other than olive oil were not introduced in significant amounts into the human diet until the early part of the 20th century. Some people believe that, as we are the genetic product of a hunter–gatherer culture, these are not natural to us as they do not match certain balances of nutrients humans had when they fed mainly on such things as grain, berries and animals and most of our fat came from animal carcasses. They go on to argue that there has not been enough time since those days for evolution to have changed the nutritional requirements of humans.
Vegetable oils used in cooking, salad oils, margarine and processed foods can supply around 15% of the total daily energy intake in a western diet. This has had the result of raising the dietary ratio of omega-6 to omega-3 fatty acids to its current value of more than fifteen to one. In hunter–gatherer diets, the omega-6/omega-3 ratio was closer to two to one.
However, recent research has indicated that there are benefits to the heart from eating fats which have a high polyunsaturate content, as many vegetable oils do. One study has suggested that for every 5% increase in polyunsaturated fat consumption there was a 10% fall in heart disease.
Some key factors which are thought by some to lead to a healthier diet are as follows:
- the ratio of omega-6 to omega-3 fatty acids.
- the erucic acid content: in 2003, Food Standards Australia set a Provisional Tolerable Daily Intake (PTDI) of about 500 mg/day of erucic acid.
- the percentage of polyunsaturates: it is recommended that adults get no more than 11% of their energy from saturated fats. Vegetable oils have an energy content of about 3700 kJ/100g.
The typical fat consumption of an adult in the EU was estimated in the year 2015 to be 143 grams per day total fat of which 30% was vegetable oils.
The table below shows the fatty acid composition of a number of common oils.
What is the polyunsaturate content of a 50:50 mixture of olive and sunflower oils as a percentage of the mass of the mixture?
Which one of the following is an assumption made in thinking that the optimal omega-6/omega-3 ratio is approximately two to one?
A The balance of nutrients that humans had when they fed on hunter–gatherer diets was more appropriate than the balance they get from modern diets.
B There were no significant differences between the diets of various hunter–gatherer groups around the world.
C The recent 10% fall in heart disease was related more to the ratio of omega-6/omega-3 than to the overall fat consumption.
D The increasing incidence of heart disease has been in line with the increased use of vegetable oils in cooking.
E Imbalances in the ratio of omega-6 to omega-3 caused by increased consumption of vegetable oils can be offset by other components of a diet.
If the only vegetable oil used by a typical European consumer is canola oil, what is his or her intake of erucic acid as a percentage of the PTDI?
What would be the percentage of flaxseed oil in a mix of flaxseed and sunflower oils if the omega-6/omega-3 ratio were two to one?
Answer: A A B D