Being overweight or obese puts extra strain on your heart. Excess body fat, especially around the waist, increases the amount of work your heart has to do to pump blood throughout the body. Just how much harder does your heart have to work if you are carrying extra pounds?
What is considered overweight or obese?
Doctors determine if someone is overweight or obese based on their body mass index (BMI). BMI is a measure of body fat calculated using your height and weight. A BMI between 25 and 29.9 is considered overweight, while a BMI of 30 or higher is considered obese.
Someone who is 5’9″ would be considered:
- Normal weight: 124 to 168 pounds
- Overweight: 169 to 202 pounds
- Obese: 203 pounds or more
The higher your BMI, the greater your health risks due to excess weight. Obesity increases your risk for many diseases and health conditions including heart disease, diabetes, high blood pressure, and stroke.
How excess weight impacts your heart
Carrying extra body fat forces your heart to pump more blood through additional tissue. This increases the workload on the heart. The extra fat also increases inflammation and oxidative stress, which can damage blood vessels and make them less elastic.
This increased strain on the cardiovascular system leads to several complications including:
- High blood pressure (hypertension): Forces the heart to pump harder to circulate blood through constricted blood vessels.
- Coronary artery disease: Plaque buildup narrows coronary arteries reducing blood flow to the heart muscle.
- Heart attack: Reduced blood supply can damage or destroy part of the heart muscle.
- Heart failure: The heart muscle weakens over time and is less able to pump blood efficiently.
Measuring heart workload
Cardiologists use several measurements to evaluate heart workload and performance. Two key measures are:
- Stroke volume – The amount of blood pumped by the left ventricle with each heartbeat.
- Cardiac output – The total volume of blood pumped by the heart per minute.
Stroke volume multiplied by heart rate gives cardiac output. The more blood the heart can pump with each beat, the less it has to work to meet the body’s demands. A lower cardiac output means the heart is straining harder to circulate blood.
Key Factors Impacting Stroke Volume
Stroke volume is influenced by:
- Ventricle filling – How much blood flows into the ventricles during diastole (relaxation phase).
- Contractility – The strength of the heart muscle contraction.
- Afterload – The pressure the heart must pump against to eject blood.
In overweight and obese individuals, increased fat tissue impairs ventricular filling. The heart is also pumping against higher peripheral resistance due to narrowed blood vessels. This decreases stroke volume and forces the heart to work harder.
Study: Impact of weight on cardiac workload
A study published in the European Heart Journal looked at the effects of obesity on cardiac workload and performance. They compared cardiac MRI data from 261 overweight or obese participants to a control group with normal BMIs. All participants were free of cardiovascular disease.
Key findings on the effect of body mass on stroke volume and cardiac output:
| BMI Category | Stroke Volume at Rest (mL) | Cardiac Output at Rest (L/min) |
|---|---|---|
| Normal Weight (BMI 18.5-24.9) | 81 | 5.5 |
| Overweight (BMI 25-29.9) | 85 | 5.9 |
| Obese (BMI ≥30) | 96 | 6.5 |
Key takeaways:
- Stroke volume was higher in overweight and obese groups.
- However, resting cardiac output was also higher indicating a greater workload.
- The obese group had an 18% higher cardiac output compared to normal weight.
The researchers concluded: “This study provides evidence that obesity is associated with maintained or enhanced cardiac performance under resting conditions, but with impaired cardiac reserve.”
Why stroke volume increases
Larger stroke volumes in overweight individuals occur because:
- The heart muscle stretches and enlarges to compensate for increased demand.
- More blood volume is required to perfuse extra fat tissue.
This increases the preload or stretch on the ventricles allowing more blood to fill the heart. So obese hearts can initially adapt by pumping more blood per beat. But this takes a toll over time leading to myocardial remodeling, chamber dilation, and eventual failure.
Impact on cardiac reserve
While stroke volume and cardiac output increase at rest in the overweight, the heart’s functional capacity declines. The obese have lower cardiac reserve, meaning their heart’s ability to increase workload in response to stress or exercise is impaired.
The heart is already working near maximal levels to perfuse excess fat tissue. This leaves limited room to further increase output as demanded by exercise or other cardiovascular stress. With less cardiac reserve, everyday activities require a higher percentage of the heart’s pumping capacity in obese individuals.
Impact of weight loss
Losing weight can significantly improve cardiac workload and function in the overweight and obese. Studies show that just a 5-10% reduction in body weight can:
- Lower blood pressure
- Improve cholesterol
- Reduce inflammation
- Decrease resting heart rate and cardiac output
- Increase exercise capacity and cardiac reserve
Even a small amount of weight loss goes a long way towards improving heart health and reversing the negative impacts of obesity on the cardiovascular system.
Conclusion
Excess body fat puts a substantial strain on the heart by increasing blood volume and forcing the heart to pump against higher pressure. Though stroke volume is often higher at rest in the obese, so is cardiac workload. Obese hearts are under chronic stress and have less reserve capacity to handle increases in demand.
Losing just 5-10% of body weight can significantly improve cardiovascular function. So if you are overweight, taking steps to slim down will take pressure off your hardworking heart.