Restricting calories severely to prolong life has been studied extensively, as discussed in the last post. Severely limiting each macronutrient group, such as total fat or total protein or total carbohydrates, has also been studied in animals. Many studies limiting total fat have shown no effect on lifespan. However, the type of fats eaten does make a big difference. A large recent study (1) involving human subjects did not limit calories at all, but simply changed the distribution of fats eaten.
The Study To Prevent Strokes And Heart Attacks
The study was done in Spain and because of this the participants already were on a Mediterranean style diet. The subjects were divided into 3 groups. One group used as a control was advised to reduce their total fat intake and shown how to do so. The other two groups were not advised to reduce any intake, but simply told about the components of the Mediterranean diet and then told to take in either more olive oil or more nuts.
It took some convincing for the two groups given more fat in their food because of the common misperception that eating more fat will make you fat. However, the follow-ups with the groups showed they did take in more olive oil and nuts. Blood tests for the markers of olive oil intake and nut intake confirmed that the two groups did get more olive oil and nuts in their diet throughout the 5 year study period.
The results were striking. Over the 5 years of the study the control group had far more strokes and heart attacks than the other two groups who ate more olive oil or nuts.
There are many interesting details in the study, but the big picture is that the individual components of a diet are important. Just looking at macronutrients as if all fats are the same or all carbohydrates are the same will not show any effect.
The control group did reduce their total fat intake – just as instructed. However, the main component reduced was monounsaturated and polyunsaturated fat. They ate the same amount of saturated fat, so the percentage of calories from saturated fat went up. Also they increased the calories from carbohydrates to make up for the calories not obtained from fat.
The two other groups increased the amount of monounsaturated and polyunsaturated fats, and reduced the amount of saturated fat in their diet. There are a large number of studies showing the deleterious effect of saturated fat. The positive effect of polyunsaturated and monounsaturated fat is not as well established, but this study confirms the value of these fats.
Potassium Was Not Studied
As with many studies looking at overall diets, the potassium and sodium content was not kept track of. However, all the participants had serious cardiovascular disease to start with, and a large percentage was already on medication for high blood pressure. The percentage of hypertensive participants in each group remained the same at the end of the study. There are several possible explanations, but very likely they were not on a high potassium foods diet.
Olive oil does not have any potassium. The potassium content of various nuts, as well as the polyunsaturated and monounsaturated fat content, can be found in a table here. A discussion of the importance of the various types of fats found in nuts and olive oil is here.
1. Estruch R, Ros E, Salas-Salvadó J, Covas MI, D Pharm, Corella D, Arós F, Gómez-Gracia E, Ruiz-Gutiérrez V, Fiol M, Lapetra J, Lamuela-Raventos RM, Serra-Majem L, Pintó X, Basora J, Muñoz MA, Sorlí JV, Martínez JA, Martínez-González MA; the PREDIMED Study Investigators, Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. N Engl J Med. 2013 Feb 25. [Epub ahead of print]