I like this study, it's the one I always call "The Spanish Study" in my head:
Distinctive postprandial modulation of β cell function and insulin sensitivity by dietary fats: monounsaturated compared with saturated fatty acids
Distinctive postprandial modulation of β cell function and insulin sensitivity by dietary fats: monounsaturated compared with saturated fatty acids
It was specifically designed to show that fat raised insulin and that saturated fat was particularly bad in this role.
It produced this graph:
Let's imagine the group leader has sketched out in advance the above graph or something like it which he wants the PhD student to aim for as their results.
Group Leader: How are you going to generate these graphs?
PhD student: Well, seems like a pot of yogurt, a slice of bread, some plain pasta and a dose of each type of fat might work...
Sadly life is not quite that simple. The insulinogenic components would need to be chosen to produce a small but measurable insulin response. Not so small as to be undetectable but not so large as to tax the pancreas or overwhelm the effect sought. Then there had to be enough fat to augment insulin secretion and generate the appropriate resistance to that signal, within the normal physiological range of pancreatic function. So the amount of fat would have to be very carefully adjusted to give an ideal amplification of the carbohydrate/protein insulin signal. In the end it turned out to be necessary to adjust the quantities of food directly to the body surface area of the participants, not a fixed meal and not even calories merely adjusted to bodyweight. The use of body surface area is normal for calculating doses for various highly toxic treatments such as chemotherapy because dosing has to be as precise as possible in this instance. Turns out this dose/surface area was needed to correctly dose the fat (50g/m2) and pasta (30g/m2) to illustrate the double bond/ROS effect. The yogurt and plain bread got a free pass.
But they did all of this successfully, got the "down" on saturated fat and polished the halo of olive oil.
I'm both impressed and grateful.
Now let's go back in time to the 1980s and look at this study:
The agenda in this study is to show that fat blunts insulin response to carbohydrate ingestion but causes delayed insulin resistance during the following meal. They threw in a butter group and a peanut butter group. Here are their results, I've chopped off the right hand end about the follow on meal as it's not relevant here:
We can also ignore the 2 X WB line which was just 480kcal of bread with a smear of cottage cheese. The lower two lines are bread alone vs the same dose of bread with some fat. Both fat sources produced results which were indistinguishable so were combined. The insulin response is exactly the same with or without fat, saturated or unsaturated..
How do you reconcile the two studies?
This second one used a fixed calorie meal with 50g of carbohydrate and 25g of protein. Fat provided around 25g for each meal.
The dose of insulinogenic substrate was well over half of the calories in the meal, the fat well under half. The total gross insulin response was to the bread, not the fat. The amount of fat was insufficient to make any detectable difference to that insulin response.
Just compare the insulin values achieved in each study, the Spanish study use a fat-free insulinogenic stimulus raising insulin from 50pmol/l up to about 70pmol/l. The bread meal raised insulin from around 70pmol/l (10mU/l) to around 400pmol/l (60mU/l), even without any added fat! There is no scope for picking up any effect of the fat, let alone from the nature of the fat. The bread effect was approaching maximal, even though it didn't quite max out the pancreas as much as the double bread meal did.
Ultimately you design your study around the result you want to generate. Sometimes it's easier than others.
The Spanish study was remarkably cleverly done but looks like they had to work hard to get the results they wanted. I still like it, even though I markedly disagree with their interpretation of the findings.
Peter
