Cortisol, also known colloquially as the “stress hormone,” is a key component of the body’s stress response system. The production of cortisol by the adrenal glands is regulated by the hypothalamic-pituitary-adrenal (HPA) axis. Disturbances in this regulation are not only involved in stress disorders and depression, but can also lead to insulin resistance and diabetes, promote obesity in the middle of the body (central or abdominal obesity, “apple type”) and silent inflammation.
Stress hormone levels: Also relevant for obesity and diabetes
In humans, cortisol levels peak in the morning and are lowest at night. Weight loss diets have a positive effect on this balance and increase morning cortisol levels (stress hormone levels). A diet high in fruit and vegetables, which is therefore higher in polyphenols and contains fewer carbohydrates, could also have a positive effect on stress hormone levels, previous research suggests. An international research team now examined the effect of the Mediterranean diet high in polyphenols (so-called green Mediterranean diet) on morning stress hormone levels and metabolic health.
Comparison of standard healthy diet, Mediterranean diet and green Mediterranean diet
In a new study, participants with obesity took part in one of three nutritional interventions for 18 months:
Standard Healthy Eating Protocol (HDG) Mediterranean Diet Green Mediterranean Diet
Both Mediterranean diets were similarly calorie-restricted and contained fewer carbohydrates than the standard healthy diet. The Mediterranean diets also contained walnuts (28 g/day). Participants on the green Mediterranean diet also received three to four cups of green tea per day and one cup of a plant-based shake. This further increased the polyphenol content of the diet. The participants’ stress hormone levels were measured between 7:00 and 7:30 a.m. at the start of the study, after six and after 18 months.
This is how the Mediterranean diet works
Strictly speaking, the Mediterranean diet is not a diet at all, but a form of nutrition. It emerged in the regions of the European Mediterranean coast, such as Italy, Greece and France. In particular, mainly
plant-based foods (fruit and vegetables) whole grain products beans nuts seafood, poultry and unsaturated fats (e.g. from virgin olive oil)
consumed. The diet is also mostly seasonal and regional. However, meat, sausage and dairy products end up on the plate less often.
Randomized, controlled long-term study over 18 months with 294 participants
A total of 294 people with an average age of 51.1 years, mostly men, took part in the study. The participants had a mean BMI of 31.3 at the start of the study. Stress hormone levels were 304.07 nmolL, with higher baseline levels in men than women. The long-term blood sugar value averaged 5.5 percent. 11 percent of participants were diagnosed with type 2 diabetes and 38 percent had prediabetes.
Higher levels of stress hormones at baseline were directly, significantly related to
the age of the participants, disorders of blood sugar metabolism, central obesity, inflammatory processes and other hormone levels (testosterone, progesterone and thyroid hormone).
In both Mediterranean diet groups, in which the dietary guidelines included calorie restriction, participants lost more weight than those on the standard healthy diet.
Weight loss:
Mediterranean diet: -2.81 percent (-2.71 kg) Green Mediterranean diet: -3.9 percent (-3.7 kg) Standard healthy diet: -0.4 percent (-0.4 ± kg)
Greater weight loss with a reduced-calorie Mediterranean diet
None of the dietary groups showed significant changes in stress hormone levels after six months. However, significant changes in morning stress hormone levels were observed in both Mediterranean diet groups after 18 months, but not in participants on the standard healthy diet.
Change in stress hormone levels after 18 months:
Mediterranean diet: -1.6 percent (-21.45 nmol/l) Green Mediterranean diet: -1.8 percent (-26.67 nmol/l) Healthy standard diet: +4 percent (-12 nmol/l)
The long-term reduced stress hormone levels were accompanied by favorable changes in fasting blood sugar, long-term blood sugar, inflammatory processes and hormone levels (thyroid hormone and testosterone), regardless of the participants’ weight loss. However, there were unfavorable changes in blood lipid levels (HDL cholesterol).
Mediterranean diet and green tea improve stress hormones and sugar metabolism
The results of the study suggest that long-term nutrition with a green Mediterranean diet higher in polyphenols (green tea and vegetable shake) may reduce morning stress hormone levels in people with obesity.
A lifestyle-related decrease in morning stress hormone levels can also have a positive effect on cardiovascular health and metabolism, independent of weight loss. The authors also report that the connection between stress hormones and blood lipid levels is unclear even based on these data.
German Health Portal / HealthCom