Can a Hot Bath Cut Blood Sugar and Burn Calories?

Monitor Blood Sugar

Story at-a-glance -

  • Hot tubs, saunas and cold baths have all been used to burn calories and normalize insulin levels
  • Benefits to using heat include improved immune system function, detoxification, increased growth hormone and more restful sleep
  • Cold thermogenesis may also improve your pain tolerance, cold tolerance, reduce food cravings and reduce overall body fat

By Dr. Mercola

Can you get the benefits of exercise without exercising? In the last century, as more people moved off small, family-owned farms to live in large cities and towns, the exercise they experienced decreased dramatically. Over the next several decades, an entire exercise industry emerged.

New fitness experts had two ways of marketing their workouts. The programs or devices were either so easy a child could do it, or they pushed you to experience limits you didn't think possible.

Using a hot tub or hot sauna after a workout was one of the strategies some used to increase their calorie burn after working out. Apparently they were on to something.

Recent research confirms that not only are more calories burned when your body temperature rises in a hot bath, but it also has a surprisingly beneficial effect on your blood sugar.

Hot Baths, Exercise and Energy Expenditure

An initial pilot study by exercise physiologist Steve Faulkner, Ph.D., measured the effect of raising core temperature on blood sugar levels and calories burned.1

A small group of volunteers were fitted with devices to monitor blood sugar, equipment to measure calories burned and rectal thermometers to measure core body temperature.

The first phase used a hot bath kept at a steady 104 degrees Fahrenheit (40 degrees Celsius) until the volunteer's body temperature had risen and stabilized. The second phase used an hour of exercise on a stationary bike.

The researchers found energy expenditure increased by 80 percent sitting in a hot bath for an hour. This didn't approach the energy expenditure from riding a bike for an hour, but was extremely close to a brisk 30-minute walk. Riding the bike burned 630 calories and the hot bath burned 140 calories in an hour.2

Heat and Peak Glucose Output

The second factor they evaluated was peak glucose output, or the rise in glucose in your blood after a meal, also called post-prandial hyperglycemia.3 The participants ate a meal of similar composition a couple of hours after their hot bath and after exercising for an hour.

Your blood sugar level after a meal is a risk marker for type 2 diabetes and metabolic syndrome. If you don't have diabetes, your pancreas secretes small amounts of insulin throughout the day in response to the amount of blood glucose and other factors.4

However, as your body becomes more resistant to insulin, the amount of glucose rises in your blood as your cells do not effectively utilize the available insulin. In Faulkner's study, the volunteers were healthy individuals without a history of diabetes. According to Faulkner:5

"What we found was that peak glucose was actually quite a bit lower after the bath, compared with exercise, which was completely unexpected."

The post-meal glucose levels were actually 10 percent lower after a hot bath than after an hour of exercise. Faulkner theorizes this may be the result of the work of heat shock proteins (HSPs) released when your body temperature rises.6

These proteins are part of your defense system and may help shunt glucose from your blood stream into your skeletal muscles, thus reducing your blood glucose levels. They are released when your body is under stress such as inflammation, infection and exercise.

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Can Heat Shock Proteins Improve Insulin Sensitivity?

This is the question researchers from the University of Kansas attempted to answer with aging mice in 1985.7 Their results were repeated successfully in more recent research.8,9 Newer technology also enabled scientists to more specifically identify HSPs responsible for skeletal uptake of blood glucose.

HSPs are involved in muscle preservation, decreasing oxidative stress and inhibiting inflammatory responses.10 Animal studies have demonstrated increasing HSP72 in mice resulted in decreased age-related oxidative stress, protection from muscle damage and from diet-induced insulin resistance.

Increasing amounts of HSP were able to improve insulin sensitivity in animal models. Although powerful, Faulkner does not suggest that a hot bath or sauna daily should replace exercise, as exercise has significantly more benefits than reducing post-meal glucose output and energy expenditure.11

From Faulkner's perspective, increasing your core temperature through hot baths and saunas would be most beneficial if you struggle with insulin resistance and controlling blood sugar, or are physically unable to exercise.

The Many Health Benefits of Heat

Hot baths and saunas (which can be designed for either wet or dry heat) have other advantages besides boosting calorie burning or improving insulin sensitivity, including:

Sweating during heavy exercise, in a hot tub or in a sauna, may help you excrete heavy metals and other toxic elements you've acquired from your environment.

Sweating helps you excrete phthalates (common in personal care products),12 cadmium, arsenic, lead and mercury.13 Researchers recommend assessing sweat as a method for evaluating the accumulation of toxins in the body as your body uses sweat to eliminate many different types.14

Saunas increase your heart rate, energy expenditure and calorie burn. Dry heat in a sauna burns more calories than a hot bath. The number of calories will depend upon your body weight, height, sex and age, but generally runs between 300 and 500 calories per 30 minute session.15 

However, weight loss you experience on the day of your sauna is usually related to fluid loss from sweating. To fully utilize the calorie burn you experience in the sauna, it's important that you not eat additional calories to offset the loss.

Saunas will increase your secretion of growth hormone,16 essential to muscle growth and health maintenance. In combination with improved insulin sensitivity, you may experience greater fat loss.17

As a sauna increases your core temperature to 38.2 degrees Celsius or just under 101 degrees Fahrenheit it stimulates your immune system.18 Other research demonstrates saunas may reduce your potential to get a cold or the flu.19

If you are looking for deeper, more relaxed sleep, look for a sauna.20 It helps relieve chronic stress and may even ameliorate symptoms of chronic fatigue syndrome.21,22

Important Safety Considerations

Each of the benefits linked to the use of hot baths and saunas results in a longer life and a reduced potential for heart disease. Researchers from the University of Eastern Finland (UEF) found an association between frequent sauna use and lower death rate from cardiovascular disease and stroke.23 But before you jump into the first sauna or hot tub you can find, there are a few safety factors you'll want to consider:

If you are going to soak in a hot bath or hot tub, make sure the water is filtered so you are not opening your pores in hot water and loading your body with chlorine, fluoride and disinfection byproducts (DBPs). If you don't have access to a filtered water tub, consider using an infrared sauna described below.

Drink plenty of water to stay hydrated. Heat stress or heat stroke are real possibilities from excessive fluid loss. The potential for the effects of significant dehydration are higher when you use a sauna after a hard workout. Carry a water bottle with you and drink frequently. But don't drink the water from a hot tub! The water is not hot enough to kill organisms, but may be hot enough to break down chlorine in a public hot tub.24  

If you experience a headache after using a sauna or hot tub, you may want to use a cool rag over your head so your body will cool more easily. Your core temperature will still rise, but the experience may be more pleasant for you.25  

If you and your wife are trying to have a baby, you'll want to steer clear of the sauna. As your body heat rises, so does the temperature of your testicles, reducing your fertility. This reduces your sperm count and motility (how well sperm swim). The effect is reversible, but can take up to five weeks.26 You'll also want to avoid the sauna during pregnancy as it may cause fetal abnormalities.27

A sauna or hot bath is supposed to be relaxing and not a torture chamber. Your body is designed to function optimally at 98.6 degrees Fahrenheit (37 degrees Celsius). Raising your core temperature above above 104.8 degrees Fahrenheit (40.4 degrees Celsius) is a medical emergency. Staying in a sauna longer than you should, or becoming severely dehydrated, can lead to death. Avoid using a sauna by yourself, always sauna with a buddy.

Your Healthiest Heat Choice

According to Rhonda Patrick, Ph.D., increasing your core temperature for short periods, as is done by using a sauna, may offer dramatic improvements to your athletic performance. She calls this concept "hyperthermic conditioning," which emerging research suggests has multiple positive effects on your body, from increased endurance to the growth of new brain cells.

Infrared saunas are a great option, and can significantly expedite the detoxification process. It heats your tissues several inches deep, which can enhance your natural metabolic processes. It also enhances circulation and helps oxygenate your tissues.

The difference between an infrared sauna and the traditional Finnish-style sauna is that the latter heats you from the outside in, like an oven. The infrared sauna heats you from the inside out, allowing for better detoxification. Steam baths are also great for detoxifying your water-based organs. So if you have lung, kidney, or bladder problems, a steam bath with some essential oil can be beneficial.

Your skin is a major organ of elimination. Unfortunately, you probably spend most of your time in a climate controlled environment and do very little sweating. Using a sauna can help restore elimination through your skin, improving detoxification, athletic performance, brain health and muscle endurance. If you've never used a sauna before, you'll want to start slowly to accommodate the detoxification process which can be significant.

If you're using an infrared sauna, heat it to 150 to 180 degrees Fahrenheit (71 to 82 degrees Celsius) and start with approximately four minutes in the sauna. Add 30 seconds to each additional sauna until you're using the sauna for 15 to 30 minutes. Finnish moist saunas are hotter, ranging from 180 to 190 degrees Fahrenheit (82 to 87.8 degrees Celsius), so the time you spend in there will typically be less.

Work your way up to 10 or 20 minutes. Infrared saunas may emit electromagnetic fields (EMF), so it's important to use a shielded sauna. You can measure the EMF from the sauna you use with a milligauss meter to ensure your safety. Health issues associated with EMF exposure may include a variety of cancers, dementia, impaired immunity and heart disease.28

To learn more about the different types of saunas available, and considerations to keep in mind when buying them, please see my interview with Steve Benda who is trained in power systems and nuclear engineering, and has spent many years designing saunas.

Is Cold as Effective as Heat?

Done correctly, cold thermogenesis may be as effective as heat to burn calories, with an added benefit.29 Exposure to cold activates brown fat tissue that can generate heat as it burns white fat found in your stomach, buttocks, hips and legs. Brown adipose tissue (BAT) is inversely related to your body mass index (BMI). In other words, the more BAT you have the lower your BMI and body fat percentage.30 Activating your BAT may increase your calorie burn and reduce your body fat.

Animal and human models have demonstrated that cold exposure may also enhance your insulin sensitivity.31,32,33,34 Frequent cold exposure may reduce your overall body fat, reduce food cravings, support your immune system and increase your pain and cold tolerance.35

If you're on beta-blocker medications (used to treat blood pressure), be sure to discuss your plans with your medical doctor before using extended heat or cold therapy. These medications can reduce your heart's ability to respond to an increased core body temperature, resulting in lightheadedness or fainting.

If you suffer from peripheral vascular disease, experience peripheral neuropathy, have diabetes or smoke, you should also consult with your physician before using either heat or cold therapy, as a reduction in blood supply to your extremities or sensation could lead to localized skin damage.

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