Cutting back on salt is often recommended to lower high blood pressure. But new research suggests this approach may have unintended harms – including increased insulin resistance, a major risk factor for type 2 diabetes.
In a new study published in the Journal of Metabolic Health, researchers James J. DiNicolantonio and James H. O'Keefe systematically reviewed findings from 23 clinical trials examining the effects of low-salt intake on markers of glucose and insulin. Across the board, the analyzed research found that restricting salt consistently led to poorer blood sugar control and increased insulin resistance.
“We discovered 23 human clinical studies showing that low-salt diets worsen markers of insulin and glucose,” said DiNicolantonio. “Caution is advised when recommending salt restriction for blood pressure control as this may lead to worsening insulin resistance.”
Some key findings from the research reviewed in the analysis:
In a new study published in the Journal of Metabolic Health, researchers James J. DiNicolantonio and James H. O'Keefe systematically reviewed findings from 23 clinical trials examining the effects of low-salt intake on markers of glucose and insulin. Across the board, the analyzed research found that restricting salt consistently led to poorer blood sugar control and increased insulin resistance.
“We discovered 23 human clinical studies showing that low-salt diets worsen markers of insulin and glucose,” said DiNicolantonio. “Caution is advised when recommending salt restriction for blood pressure control as this may lead to worsening insulin resistance.”
Some key findings from the research reviewed in the analysis:
- In healthy young men, even a moderate reduction in salt intake doubled fasting insulin levels and induced systemic and vascular insulin resistance after just 1 week. This effect was seen in men with both normal and high blood pressure.
- In patients with high blood pressure, an extreme low-salt diet significantly increased blood glucose and insulin spikes after an oral glucose tolerance test compared to a high-salt diet.
- Three months of moderate salt restriction in hypertensive patients increased insulin C-peptide levels by 40%, fasting glucose by 5.6%, and decreased HDL cholesterol by 11% – all signs of growing insulin resistance.
- One week on a low-salt diet increased insulin resistance by 15% compared to a normal-salt diet in healthy participants, when measured by the gold-standard euglycemic clamp technique.
- Among obese individuals with slightly elevated blood pressure, a low-salt intake dramatically raised fasting insulin levels and insulin response after a glucose challenge.
- Even in healthy young men, a low-salt diet for just 1 week significantly increased fasting insulin levels.
Several mechanisms may help explain why low-salt intake leads to insulin resistance, according to the analysis. For one, low salt activates the renin-angiotensin-aldosterone system (RAAS) and increases levels of stress hormones like norepinephrine. Activation of RAAS and heightened sympathetic nervous system activity are tied to insulin resistance development.
Salt restriction also reduces blood volume and blood flow to tissues like skeletal muscle. This impairs delivery of glucose and insulin to muscle tissue, worsening insulin resistance. Muscle blood flow is critical for allowing insulin to promote glucose uptake.
“Resistance to the vasodilating effects of insulin has been noted to occur in hypertension,” explained DiNicolantonio. “Insulin enhances its own ability to promote glucose uptake by its action to increase skeletal muscle blood flow.”
Beyond insulin, the reviewed research consistently found that low-salt diets raised levels of glucose, LDL cholesterol, triglycerides, and stress hormones like norepinephrine and renin. They also reduced HDL cholesterol in some cases.
“A moderate salt restricted diet seems to increase insulin C-peptide concentration substantially,” noted one study included in the analysis. “It is concluded that salt restriction may increase insulin resistance in hypertensive patients.”
Perhaps most concerning is that the blood pressure reductions seen with low-salt intake were generally small or insignificant across the reviewed studies. In fact, a subset of people saw increases in blood pressure on low-salt diets. This suggests the negative metabolic effects of salt restriction outweigh any minor blood pressure benefits.
“In the present study, the net cardiovascular risk benefit of an average blood pressure reduction of only 1.1 mmHg could well be more than offset by the rises in cholesterol, insulin, norepinephrine and hematocrit resulting from salt restriction,” concluded one study examined in the analysis.
The takeaway? Be cautious about rigid low-salt recommendations, particularly for those with, or at risk for, insulin resistance issues like obesity, high blood pressure, and diabetes. Moderate salt restriction under medical guidance may be warranted in some instances, but extreme limitation could do more harm than good.
Those worried about high blood pressure should focus first on increasing intake of potassium-rich foods like fruits, vegetables, beans, nuts, seeds, and whole grains. Potassium has been shown to lower blood pressure in clinical trials, with few risks. Weight loss, exercise, sleep, and stress reduction are also critical lifestyle factors to target first.
Before making major dietary changes, speak with your healthcare provider to develop the best blood pressure management plan for your individual health needs. Lifestyle changes should be customized based on your personal risk factors and metabolic profile.
Salt restriction also reduces blood volume and blood flow to tissues like skeletal muscle. This impairs delivery of glucose and insulin to muscle tissue, worsening insulin resistance. Muscle blood flow is critical for allowing insulin to promote glucose uptake.
“Resistance to the vasodilating effects of insulin has been noted to occur in hypertension,” explained DiNicolantonio. “Insulin enhances its own ability to promote glucose uptake by its action to increase skeletal muscle blood flow.”
Beyond insulin, the reviewed research consistently found that low-salt diets raised levels of glucose, LDL cholesterol, triglycerides, and stress hormones like norepinephrine and renin. They also reduced HDL cholesterol in some cases.
“A moderate salt restricted diet seems to increase insulin C-peptide concentration substantially,” noted one study included in the analysis. “It is concluded that salt restriction may increase insulin resistance in hypertensive patients.”
Perhaps most concerning is that the blood pressure reductions seen with low-salt intake were generally small or insignificant across the reviewed studies. In fact, a subset of people saw increases in blood pressure on low-salt diets. This suggests the negative metabolic effects of salt restriction outweigh any minor blood pressure benefits.
“In the present study, the net cardiovascular risk benefit of an average blood pressure reduction of only 1.1 mmHg could well be more than offset by the rises in cholesterol, insulin, norepinephrine and hematocrit resulting from salt restriction,” concluded one study examined in the analysis.
The takeaway? Be cautious about rigid low-salt recommendations, particularly for those with, or at risk for, insulin resistance issues like obesity, high blood pressure, and diabetes. Moderate salt restriction under medical guidance may be warranted in some instances, but extreme limitation could do more harm than good.
Those worried about high blood pressure should focus first on increasing intake of potassium-rich foods like fruits, vegetables, beans, nuts, seeds, and whole grains. Potassium has been shown to lower blood pressure in clinical trials, with few risks. Weight loss, exercise, sleep, and stress reduction are also critical lifestyle factors to target first.
Before making major dietary changes, speak with your healthcare provider to develop the best blood pressure management plan for your individual health needs. Lifestyle changes should be customized based on your personal risk factors and metabolic profile.
