The summarized study found that salt restriction either alone or in combination with a Mediterranean diet or DASH diet improved a variety of cardiometabolic risk factors independent of changes in body weight. Furthermore, combining salt restriction with a Mediterranean diet or DASH diet was better than salt restriction alone for reducing blood pressure.

These benefits are a consequence of significant changes in dietary intake in the intervention groups. The Mediterranean diet emphasizes the consumption of fruits, vegetables, pulses, nuts and seeds, wholegrains, fish, and extra-virgin olive oil; includes moderate amounts of wine, dairy products, poultry, and eggs; and contains minimal amounts of red meat, desserts and sugary beverages, and saturated fat and trans fat.^[1] The DASH diet is very similar, in the sense that it’s a plant-based diet that is rich in fruits and vegetables and contains a minimal amount of ultraprocessed foods.^[2] It differs from the Mediterranean diet in that it emphasizes the consumption of low-fat dairy products and does not emphasize the consumption of olive oil or red wine. It’s also lower in total fat.

Dietary intakes of the following nutrients differed between the control group and the 3 intervention groups at the end of the study:

	Control	Salt restriction	DASH diet + salt restriction	Med diet + salt restriction
Sodium (mg/day)	3,522	2,550	2,589	2,520
Potassium (mg/day)	2,408	2,869	3,269	3,417
Fiber (grams/day)	21	26	28	27
Saturated fat (grams/day)	31	27	22	22
Cholesterol (mg/day)	283	237	193	191

There were also important differences in dietary intake between the intervention groups. Potassium intake was higher and saturated fat and cholesterol intakes were lower in the Med diet and DASH diet groups than in the salt restriction group, intakes of monounsaturated (46 vs. 40 grams/day) and polyunsaturated fat (17 vs. 13 grams/day) were higher in the Med diet group than the DASH diet group, and calcium intake was higher in DASH diet group (1,216 mg/day) than the salt restriction group (1,017 mg/day) and Med diet group (947 mg/day).

Dietary changes can cause a lot of different effects in the body. To review the changes experienced by the participants, it can be helpful to focus on the nutrients that are most likely to influence blood pressure. First and foremost, all 3 intervention groups reduced their sodium intake by approximately 1,000 mg per day. Sodium restriction is a tried-and-true method for reducing blood pressure,^[3]^[4] with greater reductions occurring in people with higher blood pressure and higher sodium intake at baseline.

The increase in potassium intake in the intervention groups is also notable, especially with the DASH and Med diet groups, who increased their intakes by 852 and 772 mg per day, respectively. In a number of randomized controlled trials, supplementing with potassium has been found to decrease blood pressure.^[5] However, the relationship between potassium intake and blood pressure isn’t simple and is affected by sodium intake. Increasing potassium intake up to a certain point decreases blood pressure, but beyond this amount, there is either no effect or even an increase in blood pressure, in the case of very high potassium intakes and low sodium intakes.^[5]

Further demonstrating the interplay between sodium and potassium, increasing potassium intake reduces blood pressure more in people with a high sodium intake (>4,000 mg/day).^[6]

Potassium has a greater effect on blood pressure in people with a higher sodium intake

As the baseline urinary sodium level (uNa) increases (indicating higher sodium intake), so does the reduction in blood pressure with potassium supplementation. Adapted from Filippini et al., 2020, J Am Heart Assoc.

Because most people have suboptimal intakes of sodium and potassium,^[7]^[8] decreasing sodium intake and increasing potassium intake is a powerful combination for reducing blood pressure. In other research involving the use of salt substitutes (which typically comprise 75% sodium chloride and 25% potassium chloride), replacing regular salt with these products has been reported to reduce blood pressure, as well as the risks of some cardiovascular disease events and cardiovascular disease mortality.^[9]

Due to the foods they emphasize and limit, the Mediterranean diet and DASH diet are often naturally lower in sodium, and even without the specific instruction to restrict sodium intake, both of these diets have been shown to reduce blood pressure.^[10] These diets are also rich in phytochemicals, such as polyphenols, which can improve blood pressure through a variety of mechanisms.^[11]

High blood pressure is characterized by vascular dysfunction.^[12] Polyphenols have the potential to improve vascular function through their potent anti-inflammatory and antioxidant properties,^[13] as inflammation and oxidative stress are intimately involved in vascular dysfunction.^[14]

Polyphenols can also increase levels of nitric oxide in the body,^[13]^[11] which relaxes blood vessels and improves blood flow, and thus, plays a pivotal role in blood pressure regulation.^[15] Additionally, several vegetables — most notably leafy greens — are rich in nitrate, which is converted to nitric oxide in the body.

It’s also possible that polyphenols alter the composition of the gut microbiota, resulting in a decreased production of compounds that negatively affect vascular function.^[13]

The consumption of a Mediterranean diet has been shown to reduce inflammation and improve endothelial function.^[16]^[17]^[18] It’s thought that its content of extra virgin olive oil — a particularly rich source of polyphenols — contributes to many of the health benefits of the diet.^[19] A wide range of evidence indicates that supplementing the diet with extra virgin olive oil can reduce blood pressure and measures of inflammation and oxidative stress while improving endothelial function.^[20]^[21]^[22]

Additionally, increasing fiber intake has the potential to reduce blood pressure,^[23]^[24] depending on the type of fiber (soluble fiber seems to be better than insoluble fiber) and how much intake is increased by.

In summary, sodium restriction is an effective method for decreasing blood pressure, but combining sodium restriction with the Mediterranean diet or DASH diet results in a greater decrease in blood pressure. This is mostly due to an increase in the intake of potassium and phytochemicals. An increase in fiber intake, as well as other micronutrients (e.g., magnesium, calcium), also likely contributes.

Going beyond salt restriction to reduce blood pressure Original paper