Hypertension

Effects of a high-carbohydrate diet on blood pressure:

1. Salt

In my post about salt (Salt - Is it the Cause of Hypertension?) I explained how little blood pressure will be reduced by eliminating salt from the diet.

In short, this mechanism is as follows:

• high-carbohydrate and sugar diet ->
• kidney unable to excrete salt ->
• high salt concentration in the body ->
• water retention to dilute excessive salt ->
• hypertension

In this case, the best solution would be to reduce carbohydrates and sugar, to allow the kidneys to excrete water along with salt, leading to the return of a normal blood pressure. The currently recommended low-salt diet will help reduce blood pressure by only a few units (mm Hg), water retention will still be a problem.

Hypertensive drugs (known as diuretics) given to people with high blood pressure, have exactly the same effects as a low-carbohydrate diet, prompting the kidneys to get rid of water and salt.

Salt is a very important component of a healthy diet. It is necessary for normal cell function.

2. Central nervous system

In the 1970s, Lewis Landsberg noted that insulin has the same stimulating effect on the central nervous system as adrenaline (stress hormone). When adrenaline or insulin is high, it stimulates the flight-or-fight response in the brain, resulting in the increase of the heart-rate and blood pressure. 

By this logic, if insulin levels remain chronically high (by eating a high-carbohydrate diet), the nervous system is constantly stimulated to constrict blood vessels, leading to elevated blood pressure. The higher the insulin levels, the greater the risk of heart disease.

3. Metabolic syndrome

The accepted path to diabetes is the following:

• A diet high in sugar and refined carbohydrates (glucose) ->
• Chronically high insulin levels ->
• Inability of the muscle to utilize glucose as fuel (metabolic syndrome) ->
• Diabetes

Diabetics have a very high risk of developing heart disease. This implicates that anything contributing to diabetes, will also play a role in the development of heart disease.

"Insulin and blood pressure are closely related in both normotensive and hypertensive people. Although obesity and diabetes are often found in hypertensive people, hyperinsulinemia also occurs in nonobese nondiabetic hypertensive people. Thus, hyperinsulinemia [high insulin level] is closely associated with a cluster of cardiovascular risk factors, i.e., hypertriglyceridemia [high triglyceride level], low HDL levels, hypertension, hyperglycemia, and upper-body obesity."
                                                                                - Robert W. Stout, MD

As insulin is a hormone responsible for fat storage in the fat tissues, it has the same effect on blood vessels. Insulin stimulates the wall of the arteries to store fat and cholesterol in the lining, leading to atherosclerosis [build-up in the arteries].

In a few words, these are the steps:

1. high carbohydrate and sugar diet
2. high insulin levels
3. atherosclerosis
4. heart disease

"This means that anything that raises blood sugar [...], will lead to more atherosclerosis and heart disease, more vascular disorders, and an accelerated pace of physical degeneration, even in those of us who never become diabetic."
                                                                                 - Gary Taubes

4. Lipid profile

Today, the best biomarkers of heart disease are:

• high triglyceride level
• low HDL (good cholesterol)
• high LDL (bad cholesterol). The size of the LDL matters: the smaller the LDL size, the greater the risk of heart disease. Big size LDL is not a risk factor for heart disease.

Total cholesterol does NOT predict heart disease.

This mechanism in short is (Cholesterol: The Dangers of Low-Fat Diets):

• high-carbohydrate diet ->
• high triglyceride level ->
• high number of VLDL, which will end it's life in a ->
• high number of small size LDL ->
• biomarker for heart disease

"Both insulin resistance and high carbohydrate intakes have been shown to contribute to [...] dyslipidemia [abnormal amount of cholesterol and fat in the blood], and refined carbohydrates, in particular, can raise triglyceride and lower HDL cholesterol concentrations. Of interest, reductions in dietary carbohydrate, even in the context of a diet high in saturated fat, have been associated with reduced concentrations of small, dense LDL."
- Patty W. Siri-Tarino, Qi Sun, Frank B. Hu, and Ronald M. Krauss: Saturated Fatty Acids and Risk of Coronary Heart Disease: Modulation by Replacement Nutrients

I would like to repeat: "even in the context of a diet high in saturated fat, have been associated with reduced concentrations of small, dense LDL."

This means that a no matter how high the diet is in saturated fat, it has no effect on the elevation of small size LDL.