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What Causes What
MECHANISM− DECREASES

Mediterranean diet → Insulin resistance (HOMA-IR)

Higher Mediterranean diet decreases Insulin resistance (HOMA-IR).

In 418 older Spaniards free of diabetes, PREDIMED-Reus assigned a Mediterranean diet with free extra-virgin olive oil or mixed nuts against low-fat advice. After a median four years the pooled Mediterranean arms had about half the new type 2 diabetes (hazard ratio 0.48). The measure is diabetes incidence, not HOMA-IR.

Randomized trial · Moderate · N=418

Supported by an experiment or a tightly identified design. Read the caveats.

Mechanism

The PREDIMED authors treat the Mediterranean pattern as a high-unsaturated-fat diet: olive oil as the main fat, vegetables, fruit, legumes, nuts, fish, and modest wine, with less red meat, butter, pastry, and sweet drinks. They think that fat swap, plus the phenolics in extra-virgin oil and nuts, improves how insulin works without a calorie deficit. In Reus, weight and leisure activity barely moved. Salas-Salvadó, Bulló, Babio and colleagues nested a diabetes endpoint in one PREDIMED center. 418 people aged 55 to 80, free of diabetes, high cardiovascular risk. They were assigned to low-fat advice, a Mediterranean diet with a liter of virgin olive oil a week, or the same diet with 30 grams of mixed nuts a day. No calorie target. No exercise program. Diabetes was fasting glucose at or above 7.0 mmol/l or two-hour glucose at or above 11.1 mmol/l after a 75-gram load, confirmed on a second test, by a committee blinded to assignment. Median follow-up was 4.0 years. Fifty-four people developed diabetes. Rates per 1,000 person-years were 24.6 (olive oil), 26.8 (nuts), and 46.6 (control). Multivariate hazard ratios versus control were 0.49 (0.25 to 0.97) for olive oil and 0.48 (0.24 to 0.96) for nuts. Pooled, 0.48 (0.27 to 0.86). Baseline HOMA-IR was recorded in 307 people. It was not the outcome. Martínez-González, Montero, Ruiz-Canela and colleagues later scored yearly Mediterranean Diet Adherence Screener points in 3,541 PREDIMED participants who started without diabetes. Two extra points on the cumulative average sat with hazard ratio 0.80 (0.70 to 0.92) for new diabetes. Highest versus lowest score (12 to 14 versus under 8) sat at 0.46 (0.25 to 0.83). Adjusting for the randomized arm left 0.82 per two points and 0.48 for the extremes. Two hundred seventy-three incident cases. That is attained adherence inside the same trial, not a second assignment.

Caveats

The insulin page on this site is named for HOMA-IR. PREDIMED-Reus identified new type 2 diabetes. Do not read the stamp as a HOMA change. Reus is one Spanish center, older people at high cardiovascular risk, 54 events. Seventeen percent of scheduled oral glucose tests were refused. Forty-one people had none, so some diagnoses rest on fasting glucose only. The control arm was told to cut fat and mostly did not. Staff who collected diet and weight knew the assignment. Olive oil and nuts were donated by producers. A 2018 erratum said PREDIMED's individual randomization slipped for at most 14 percent of the whole trial. Reus was not the clinic-assignment site. Twenty-nine Reus household second members (6.9 percent) were put on a spouse's arm. Dropping them left a pooled hazard ratio of 0.47 (0.26 to 0.87). The 2023 paper is yearly attained score, not intention-to-treat. Residual confounding remains after adjusting for the arm. This is a journal entry, not medical advice and not a reason to buy oil, nuts, or a scorecard.

Effect

odds_ratio = 0.48. PREDIMED-Reus multivariate HR 0.48 (0.27-0.86) pooled MedDiets vs low-fat. 54 T2D events in 418. 2018 household-drop HR 0.47. Incidence, not HOMA.

Nodes

Lifestyle & environmentMediterranean dietBiology & endocrinologyInsulin resistance (HOMA-IR)

Named confounders

Cite this page

What Causes What. “Mediterranean diet → Insulin resistance (HOMA-IR).” https://whatcauseswhat.org/edges/e-med-insulin (atlas updated 2026-09-02).

https://whatcauseswhat.org/edges/e-med-insulin

Papers