Caloric restriction mimics the positive effects of beta-blockers on the heart

This article features a study that showed that caloric restriction has the same benefits that beta-blockers provide to failing hearts.

Beta-blockers like metoprolol and atenolol are recommended for people with congestive heart failure (CHF). Failing hearts cannot supply enough blood. That is why people with CHF constantly feel weak and short of breath.

In heart failure, the sympathetic nervous system tries to compensate for the failing heart but, in the end, makes the cardiac function worse.

Greater sympathetic discharge leads to a rapid heart rate and higher blood pressure. Both contribute to heart failure.

That is the reason why beta-blockers, which inhibit excessive sympathetic discharge, are used in CHF.

Previous studies have shown that dietary caloric restriction has decreased sympathetic discharge, but this study from Germany found more positive cardiac effects.

Experiment protocol

There were four groups of Wistar rats studied.

Caloric restriction CR (− 40% kcal, three months)
Beta-blocker – metoprolol succinate (250 mg/kg BW/day)
Diuretic (water pill) – furosemide (15 mg/kg BW/day) – Diuretics are commonly prescribed in heart failure patients to remove excess water.
The Control group had a regular diet

Results

A. The left ventricular (LV) systolic function improved markedly in the caloric restriction group. Mildly in the beta-blocker group but deteriorated in the diuretic and control group.

The left ventricle is the chamber of the heart that pumps blood to the whole body except for the lungs. The right ventricle supplies the lungs.

Systole is the phase of the heartbeat when it contracts and pumps blood.

If the systolic function of the left ventricle decreases, not enough blood comes out, and the animal will feel weak. Fluid will start to back up in the lungs causing shortness of breath.

Caloric restriction improved the heart’s contraction more than the beta-blockers.

B. Diastolic function was preserved by caloric restriction and beta-blocker but impaired by diuretics.

Diastole is when the heart relaxes, and blood fills its chambers. A normal, compliant heart can fully relax and fill up with enough blood for the next contraction.

In heart failure, the cardiac muscles become stiff and cannot distend to fill with enough blood. That is called diastolic dysfunction.

Diastolic dysfunction decreases the amount of blood delivered to the body resulting in easy fatigue. The consequence is that the heart calls on the sympathetic nervous system to make the heart faster to make up for the decrease in blood delivery.

The rapid heart rate shortens the diastolic phase and decreases cardiac output.

That creates a vicious cycle that makes heart failure worse. The beta-blockers are used to prevent the vicious cycle.

By preserving diastolic function, caloric restriction may be a promising substitute for beta-blockers in heart failure.

The heart showing valves, arteries, and veins. The white arrows show the normal direction of blood flow. Source: Wapcaplet

C. Caloric restriction reduced blood pressure identical to diuretics and beta-blockers.

Another effect of the sympathetic nervous system is to increase blood pressure by constricting the arteries. Narrower arteries result in higher pressures the failing heart has to work against. The increase in cardiac work worsens heart failure.

Lower blood pressure from caloric restriction relieves the failing heart.

D. Caloric restriction was identical to beta-blockers in reducing heart rate.

Slowing the heart rate allows more time for the heart to relax and fill with more blood for the next contraction. More blood supplied with each cardiac contraction relieves the heart failure symptoms and further decreases the stress and sympathetic discharge.

D. Plasma noradrenaline was decreased by caloric restriction and beta-blockers but increased by the diuretics.

Noradrenaline is the chemical used by the sympathetic nervous system. Lower noradrenaline means a systemic decrease in sympathetic discharge, slower heart rate, and lower blood pressure.

E. Caloric restriction reduced left ventricular oxidative damage and apoptosis

You may have heard of heart disease as a result of chronic inflammation. One cause of inflammation is the production of unstable free radicals that cause cell damage and destruction.

This study shows that caloric restriction prevents early cell death or apoptosis and preserves cardiac muscle.

F. Caloric restriction increased mitochondrial biogenesis

The mitochondria produce energy for cellular function. The heart muscles never stop working and need a constant supply of adenosine triphosphate (ATP). With time, mitochondria get worn out and cannot supply enough ATP.

Caloric restriction allows for mitophagy or mitochondrial autophagy. Autophagy is when old organelles inside the cell, like the mitochondria, are recycled to make new and well-functioning mitochondria.

Caloric restriction leads to more fuel for the heart muscles.

Can the results apply to humans?

Several human randomized-controlled trials show that caloric restriction improves essential hypertension, fast heart rate, low heart rate variability, sympathetic nervous system dominance over parasympathetic, arterial stiffness, endothelial dysfunction, and poor flow-mediated arterial dilatation.[2]

The improvement of all the parameters normalizes blood pressure and allows patients to discontinue antihypertensive medications.[2]

Caloric restriction appears effective regardless of age, gender, ethnicity, weight, body mass index, metabolic syndrome, or type 2 diabetes diagnosis. The greatest benefit is usually observed in the sickest subjects, and blood pressure may continue to improve during the refeeding period.[2]

Caution

Don’t overdo caloric restriction. A study on rats fed with a very low-calorie diet (60% caloric reduction) resulted in vascular problems and cardiac arrhythmias.[3]

Talk to your doctor before starting any diet. If you are hypertensive or diabetic, blood pressure and glucose may need monitoring. Some diabetes, heart, and antihypertensive medications may need to be adjusted.

Note: This article seems like a good follow-up to Antiplatelets and beta-blockers increase heart attacks in 25-59-year-olds in warm weather that I published earlier today.

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Related:

Intermittent fasting is similar to caloric restriction. I like intermittent fasting better.

References:

Niemann, B., Li, L., Simm, A. et al. Caloric restriction reduces sympathetic activity similar to beta-blockers but conveys additional mitochondrio-protective effects in aged myocardium. Sci Rep 11, 1931 (2021). https://doi.org/10.1038/s41598-021-81438-7
Nicoll R, Henein MY. Caloric Restriction and Its Effect on Blood Pressure, Heart Rate Variability and Arterial Stiffness and Dilatation: A Review of the Evidence. Int J Mol Sci. 2018 Mar 7;19(3):751. doi: 10.3390/ijms19030751. PMID: 29518898; PMCID: PMC5877612.
Almeida, J. F. Q. et al. Short-term very low caloric intake causes endothelial dysfunction and increased susceptibility to cardiac arrhythmias and pathology in male rats. Exp. Physiol. 105, 1172–1184. (2020).

Image credit: The heart by Wapcaplet – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=830253

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