High blood pressure is sometimes called the "silent killer" because people often don't have any signs or symptoms. Unfortunately, high blood pressure can have far-reaching health implications. Therefore, it's essential to understand how your diet affects your blood pressure, and eating a meal or not eating is just one of the many factors affecting your blood pressure.
Blood pressure is a measurement of the force that blood flows through your circulatory system. Blood pressure readings consist of two parts:
Systolic pressure is a measurement of the force of blood through your arteries each time your heart pumps.
Diastolic pressure is a measurement of the force of your blood when your heart relaxes between beats, and the ventricles are allowed to refill with blood.
Your blood pressure results are given in two numbers. These numbers represent the systolic pressure over the diastolic pressure number. For example, if your systolic pressure is 120 and your diastolic pressure is 80, your blood pressure will be stated as "120 over 80" and recorded as "120/80." Your blood pressure reading results are then used to classify your blood pressure as normal, high, or low.
It's normal for your blood pressure to rise and fall. Research shows that blood pressure has short-term fluctuations throughout the day and long-term fluctuations over time.¹ Your blood pressure can fluctuate with every heartbeat. Thus, they can change every minute, day, week, month, year, and depending on the season.
For this reason, most doctors consider the results of several blood pressure readings before making a diagnosis. Typically, your doctor will average two or more readings from several visits before determining if your blood pressure could be an issue. In some cases, they may also ask that you track your blood pressure at home to ensure the most accurate results.
Several factors can affect your blood pressure, including the anxiety of visiting a doctor. However, in a healthy person, blood pressure always stays within a normal range. For most adults, normal blood pressure is a systolic pressure of less than 120 with a diastolic pressure of less than 80, or 120/80. Low blood pressure, also known as hypotension, is a reading lower than 90/60, while high blood pressure, or hypertension, is defined as a reading higher than 130/80.
Older adults sometimes develop an issue known as isolated systolic hypertension, where their systolic pressure is 130 or higher, while their diastolic pressure remains below 80. This common blood pressure issue is age-related and caused by stiffening of the major arteries.
If your blood pressure readings are outside of the normal range, your doctor will work to identify and treat the cause of your condition. They will likely take a comprehensive history and perform a complete physical examination, and request various blood tests. They may also utilize various other diagnostic tools such as:
Ambulatory blood pressure measurement
Ambulatory blood pressure measurement is a common tool used to monitor and diagnose high blood pressure. The device is attached to a strap or belt and automatically inflates and takes a measurement, typically every half hour for a 24-hour period. The data is collected and later transferred to a computer.
An electrocardiogram, also referred to as an EKG or ECG, is a non-invasive and painless test. Electrodes are attached to your arms, legs, and chest during the test. These electrodes measure your heartbeat’s electrical activity, rate, and rhythm and record the results on a paper graph.
An echocardiogram is a painless test that uses sound waves to take pictures of your heart's valves and chambers. The test allows doctors to measure the chambers and wall thickness and study the pumping action of your heart.
If your doctor is concerned about your blood pressure, he may suggest tracking it at home. Typically, they will ask that you take a measurement twice a day at the same time every day and that you take two or three readings each time to ensure accuracy.
Doctors usually suggest that your first blood pressure reading of the day be done in the morning, shortly after waking. However, people often wonder if they will have high blood pressure when hungry.
Your blood pressure is usually at its lowest when you sleep and begins to rise a few hours before you wake. After that, it typically rises throughout the day, peaking around midday before dropping in the afternoon and evening.
Morning is the highest risk period of the day for cardiovascular events, especially heart attacks and strokes. In addition, while blood pressure usually peaks by midday, the morning is associated with a rise in blood pressure.² People with high blood pressure experience a more significant increase and a greater rising rate.
While your blood pressure may decrease after eating breakfast, this morning reading is critical for identifying abnormal blood pressure patterns. Abnormal blood pressure patterns include high blood pressure during the night or early in the morning or a less than 10% drop in blood pressure overnight. A rise in blood pressure overnight to early morning is associated with an increased risk of heart disease.
You can prepare for your day as usual but don't eat, exercise, or take any medication until after measuring your blood pressure.
Often, your blood pressure is higher before eating because after you eat, blood pressure typically drops as blood is diverted to the digestive system. While eating a meal usually causes a slight drop in blood pressure, intermittent fasting sometimes lowers blood pressure.³ However, fasting can also cause an electrolyte imbalance that can lead to issues with the rhythm of your heartbeat.
Your blood pressure can also be affected by severe malnutrition or starvation, where your body is deprived of adequate nutrition.⁴ While starvation is an unusual state, research shows a gradual decrease in blood pressure during the first three days of fasting, but the heart rate does not change.
Typically, your blood pressure tends to drop slightly after eating a meal. This decrease in blood pressure occurs because your body directs extra blood to the stomach and small intestine after you eat. This diversion of blood flow causes a temporary reduction in blood pressure throughout the rest of your body.
As your body begins to respond, blood vessels outside the digestive system constrict. This narrowing of the blood vessels causes your heart to compensate by beating faster and harder to maintain blood flow and healthy blood pressure in your brain, extremities, and body.
If your heart and blood vessels don't respond correctly when the extra blood is directed to your digestive system, your blood pressure will decrease everywhere but in the digestive tract. This drop in blood pressure can result in a condition known as postprandial hypotension, which can cause:
Temporary loss of consciousness
Severe chest pain
According to a 2010 review of research, postprandial hypotension may affect nearly 33 percent of older adults living in nursing homes.⁵
While a person's blood pressure usually drops slightly after eating a meal, certain foods can increase blood pressure, and in some people, this increase exceeds the normal range. This sudden increase in blood pressure is often referred to as a blood pressure spike. A sudden and extreme increase in blood pressure can lead to severe complications, including kidney failure, stroke, and heart attack.
For instance, eating foods with a high salt content can cause a temporary blood pressure spike. Salt is primarily composed of sodium, a mineral that occurs naturally in many foods, but too much can cause your blood pressure to rise.
While salt is one of the most common sources of sodium, other food additives, such as monosodium glutamate, often referred to as MSG, also add sodium to your diet. When your diet has too much salt, your body retains extra water to remove the sodium from your body. The added moisture in your body places added stress on the heart and blood vessels and, in some people, causes their blood pressure to rise suddenly.
Here are some warning signs and symptoms of high blood pressure that may be life-threatening:
Severe chest pain
Severe headache, accompanied by confusion and blurred vision
Nausea and vomiting
Shortness of breath
High blood pressure can have many contributing factors but is classified as one of two types.
Primary hypertension, also called essential hypertension, is the most common type of high blood pressure and develops gradually over many years. However, for most adults, there is no identifiable cause.
Secondary hypertension is high blood pressure resulting from an underlying condition. This type of high blood pressure typically occurs in patients under 30 years of age and is more resistant to blood pressure treatments. Secondary hypertension can be the result of various conditions and medications, including:
Renal artery stenosis
Renal parenchymal disease⁶
Coarctation of the aorta
Obstructive sleep apnea
Medications, including birth control pills, cold remedies, decongestants, over-the-counter pain relievers, and some prescription drugs
Illegal drugs, including cocaine, ecstasy, and amphetamines
In addition to medical conditions, your blood pressure can read high for many other reasons. If you monitor your blood pressure at home, you should avoid tobacco, caffeine, and food for at least 30 minutes before you take your blood pressure.
When you are ready to measure your blood pressure, find a comfortable spot where you can sit quietly for a few minutes. Sit with your legs and ankles uncrossed and your back supported against a chair. Stay calm and relaxed and not think of stressful things. Avoid talking while measuring your blood pressure. Also, use the bathroom first because a full bladder can slightly increase your blood pressure.
Other factors that can affect your blood pressure monitoring include the following:
You should take your blood pressure before exercising because measuring it after physical activity may give you an elevated reading.
Digesting food can lower your blood pressure, so take your blood pressure before eating in the morning, and if you have to eat first, wait at least 30 minutes before taking a reading.
Inaccurate readings can result from the cuff of your blood pressure monitor not fitting your upper arm properly.
Your clothing can affect the results of your blood pressure reading. The cuff must be placed over bare skin, and if you roll up your sleeve and it's tight on your arm, you need to take your arm out of the sleeve or remove the shirt.
You may get a higher blood pressure reading if you're cold.
Your arm should rest on a table or the arm of a chair, at about the same height as your heart. The cuff should be placed on your bare upper arm, about one inch above the bend of your elbow, and you should sit with your back supported in a chair and your legs uncrossed. Always use the same arm and position to ensure consistent and comparable results.
It's also essential to ensure the accuracy of your home blood pressure monitor. You should bring your home monitor to your doctor's office once a year or anytime you may have concerns about its accuracy. While there, you can compare measurements from your monitor with readings from your doctor's equipment.
Getting an accurate blood pressure reading is critical to prevent heart attacks or strokes and heart and brain damage in the event that your blood pressure is too low. Many factors affect your blood pressure and the accuracy of blood pressure readings. Diet, stress, lifestyle, and even eating or not eating can influence its accuracy.
If your blood pressure is regularly outside of the normal range, your doctor will want to monitor it closely, which may involve home monitoring. If you measure your blood pressure at home, it's critical to take the readings consistently. You should also avoid alcohol, tobacco, caffeine, or exercise before reading your blood pressure and not measure it too soon after eating a meal.
High blood pressure and older adults | National Institute on Aging
Systolic hypertension (2022)
How to provide ambulatory blood pressure monitoring for patients | The Pharmaceutical Journal
Electrocardiogram | National Heart, Lung, and Blood Institute
Echocardiography | National Heart, Lung, and Blood Institute
Essential hypertension (2000)
Renal artery stenosis | National Institute of Diabetes and Digestive and Kidney Diseases
Primary hyperaldosteronism | Genetic and Rare Diseases Information Center
Pheochromocytoma | National Cancer Institute
Cushing's syndrome | National Institute of Diabetes and Digestive and Kidney Diseases
Coarctation of the aorta (2022)
Obstructive sleep apnea (2022)
Want all the latest clinical trial and HealthMatch news in your inbox? We thought you might! Sign up below.
Want all the latest clinical trial and HealthMatch news in your inbox? We thought you might! Sign up below.