Restricting calories severely to prolong life has been studied extensively, as discussed in the last post. Similarly, researchers have studied the effect in animals of severely limiting each macronutrient group, such as total fat or total protein or total carbohydrates. Many studies limiting total fat have shown no effect on lifespan. However, the type of fats eaten does make a big difference. For example, 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. Researchers divided the subjects into 3 groups. Then they advised members of one group, used as a control, to reduce their total fat intake, and showed them how to do so. They did not advise the other two groups to reduce any intake, but simply told the groups about the components of the Mediterranean diet. Then they told the members of the 2 groups to take in either more olive oil or more nuts.
It took some convincing for the two groups given more fat in their food to eat more fat. The common misconception that eating more fat will make you fat is difficult to overcome. 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.
And 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.
The study includes many interesting details. 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. Furthermore, 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.
In contrast, the two other groups increased the amount of monounsaturated and polyunsaturated fats. And they reduced the amount of saturated fat in their diet. There are a large number of studies showing the deleterious effect of saturated fat. However, 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 researchers did not keep track of the potassium and sodium content. However, all the participants had serious cardiovascular disease to start with, and a large percentage were already on medication for high blood pressure. In comparison to the start of the study, 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 the participants were not on a high potassium foods diet.
Olive oil does not have any potassium. The potassium content of various nuts is usually high. Also, if unsalted, nuts have a high potassium to sodium ratio. Their potassium and sodium values can be found in the nuts table. The table can be accessed by clicking the tab at the top of the page labeled “Links to Food Potassium Tables”.
Republication Of Study
Because of irregularities in the randomization procedure in the original article, the authors re-analyzed their data. And they retracted the original article and republished their article. See (2) for the irregularities statement and (3) for the republication. However, the conclusions remain unchanged.
1. Primary prevention of cardiovascular disease with a Mediterranean diet. Estruch R1, Ros E, Salas-Salvadó J, Covas MI, 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; PREDIMED Study Investigators. N Engl J Med. 2013 Apr 4;368(14):1279-90. doi: 10.1056/NEJMoa1200303. Epub 2013 Feb 25.
2. Retraction and Republication: Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. N Engl J Med 2013;368:1279-90. Estruch R1, Ros E2, Salas-Salvadó J3, Covas MI4, Corella D5, Arós F6, Gómez-Gracia E7, Ruiz-Gutiérrez V8, Fiol M9, Lapetra J10, Lamuela-Raventos RM11, Serra-Majem L12, Pintó X13, Basora J14, Muñoz MA14, Sorlí JV5, Martínez JA15, Martínez-González MA15. N Engl J Med. 2018 Jun 21;378(25):2441-2442. doi: 10.1056/NEJMc1806491. Epub 2018 Jun 13.
3. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. Estruch R1, Ros E1, Salas-Salvadó J1, Covas MI1, Corella D1, Arós F1, Gómez-Gracia E1, Ruiz-Gutiérrez V1, Fiol M1, Lapetra J1, Lamuela-Raventos RM1, Serra-Majem L1, Pintó X1, Basora J1, Muñoz MA1, Sorlí JV1, Martínez JA1, Fitó M1, Gea A1, Hernán MA1, Martínez-González MA1; PREDIMED Study Investigators. N Engl J Med. 2018 Jun 21;378(25):e34. doi: 10.1056/NEJMoa1800389. Epub 2018 Jun 13.