Nancy A. Melville
May 20, 2021
Older people with prediabetes who followed a diet rich in sardines for 1 year show significant reductions in risk of developing type 2 diabetes compared with those placed on a similarly healthy diet but without the sardines, results from a new randomized trial show.
"A 1-year, sardine-enriched type 2 diabetes-preventive diet in an elderly population with prediabetes exerts a greater protective effect against developing type 2 diabetes and cardiovascular events, by improving anthropometric parameters, blood chemistry profile, lipid composition in erythrocytes membranes, and metabolomics data," report the authors in research published in Clinical Nutrition by Diana Diaz-Rizzolo, PhD, of the Hospital Clinic of Barcelona, Spain, and colleagues.
While cardiovascular and other health benefits of unsaturated fats in oily fish are well-established and are a key component in diets such as the highly recommended Mediterranean diet, the authors note that the consumption of sardines for the prevention of type 2 diabetes has not previously been studied.
In addition to being rich in healthy omega-3 fatty acids, sardines have high concentrations of taurine — approximately 147 mg per 100 g serving — which, depending on the sardine species, is believed to have hypoglycemic, antioxidant, and anti-inflammatory benefits, the authors note.
Participants Advised to Consume the Whole Sardine, Bones and All
To evaluate the effects, researchers enrolled 152 patients aged 65 and older who had been diagnosed with prediabetes (blood glucose levels between 100-124 mg/dL) and placed them all on a nutritional program to reduce the risk of diabetes for 1 year.
In addition, about half (n = 75) were also instructed to consume 200 g of canned sardines in olive oil per week, in 100 g servings consumed twice per week.
Those participants were recommended to consume the entire sardine, without removal of bones, due to their rich content of calcium and vitamin D. They were also provided with recipes that used canned sardines.
At 1 year, the percentage of participants classified as being at a very high risk of type 2 diabetes, assessed by the Finnish Diabetes Risk Score (FINDRISC), compared with baseline, had declined to a much greater degree in the sardine consumption group (37% at baseline vs 8% at 1 year) compared with those in the control group, who only consumed the nutritional diet (27% vs 22%) (P = .021).
In addition, those in the sardine group had greater increases in healthy HDL cholesterol and the glucose-regulating protein hormone adiponectin, with decreases in triglycerides compared with the nonsardine group (all P < .005).
Furthermore, the sardine consumption group had a greater decrease in insulin resistance, assessed by Homeostatic Model Assessment for Insulin Resistance (HOMA-IR; P = .032).
Sardines Are Cheap and Reduce Blood Pressure Too
"Not only are sardines reasonably priced and easy to find, but they are safe and help to prevent the onset of type 2 diabetes," said Diaz-Rizzolo in a press statement.
Those in the sardine group also showed significant decreases in systolic blood pressure (P = .014) and diastolic blood pressure (P = .020) versus baseline, while no significant changes were observed in the control group. The authors suggest that sardines' rich taurine concentrations could play a role in those effects.
"Previously, only lean fish consumption had demonstrated an improvement in blood pressure, not fatty fish consumption, perhaps because the species studied excluded those with a higher taurine content such as sardines," they speculate.
In addition to showing improvements in levels of taurine, those in the sardine group also showed increases in nutrients that have been linked to health benefits, including omega-3 EPA and DHA, vitamin D, and fluorine (all P < .05).
The authors note that the increases could be attributed to sardines' rich concentration of those nutrients, as well as to the olive oil that is present in the sardine can.
Some Benefits Seen in Both Groups
The patients in the study were a mean age of 71 and had been in a prediabetic state for an average of 4.8 years at the beginning of the study. They were 55% male and there were no other significant differences in characteristics between the groups.
While the conversion from being prediabetic to type 2 diabetes in the adult population has been reported to be about 10.6%, and the risk has been observed to be even higher in the 65 and older population, rates were lower than that in both groups.
"At the end of our 1-year study, we observed a [rate of] new-onset type 2 diabetes of 2.7% and 5.2% in the sardine group and control group, respectively," the authors note. They add the differences were not statistically significant.
Both the sardine consumption and control groups showed significant reductions in A1c versus baseline (P = .011 and P = .010, respectively), as well as significant reductions in glucose fasting concentrations (P = .020 and P = .040, respectively).
And while the sardine group showed greater improvements in HDL versus the control group (P = .045), only the control group showed a significant decrease in total cholesterol versus baseline (P = .032).
Both groups showed improvements in the management of body weight, body mass index, and waist and hip circumference, in addition to improvement in body composition — despite no physical activity components in the programs, the authors note.
"This is probably because both groups followed the same base type 2 diabetes-preventive diet, with the one exception of sardine supplementation, and, although they did not modify their physical activity, both groups reduced their daily caloric intake through food," the authors note.
The possibility of reducing diabetes risk through dietary changes as opposed to weight loss is especially important in the older population, the authors note, as some studies suggest a link between weight loss in the elderly and an increased risk of mortality.
In a second phase of the study, the researchers say they are evaluating the effect of sardines on the intestinal microbiota, "since it affects the regulation of many biological processes, and we need to understand if they have played a part in this protective effect against type 2 diabetes," Diaz-Rizzolo concluded.
The study was funded by RecerCaixa 2013. The authors report that " no industry sponsorship was received for this work that could have influenced its outcome."