When’s the Best Time to Eat? Your Body Clock Knows


Two teenager girls, sisters, eats fastfood on the street

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The American Heart Association recently released a statement suggesting that when and how often you eat could affect your risk for developing heart disease and stroke. Until now, the focus on diet has been primarily about how much and what you eat. This news—that the time of day you eat may also be important—could change the way people are able to manage their health.

Our bodies have natural daily patterns called circadian rhythms that occur roughly over a 24-hour cycle. Many biological processes are driven by circadian rhythms, including when you go to sleep and wake up, your body temperature, heart rate, blood pressure and the release of various hormones. A “master clock,” a tiny group of cells called the suprachiasmatic nucleus (SCN), located in the hypothalamus area of the brain manages circadian rhythms. This master clock is mostly controlled by changes in light.

Every cell in the body also has its own internal clock called a “peripheral clock.” Peripheral clocks make sure all of the cells’ functions are coordinated with the master clock. Animal studies show us the importance of keeping peripheral clocks in sync with the brain’s master clock. For example, when the peripheral clock in a mouse’s heart is disrupted, the mouse develops heart failure and dies at a much younger age than normal mice.

Unlike the master clock, peripheral clocks are more responsive to the availability of food than changes in light. As a result, eating at the “wrong” time of day could shift the rhythms of the peripheral clocks so they are out of sync with the master clock. For example, shift workers who work in the middle of the night are active when they would normally be asleep and eat at times when their body doesn’t expect food. They are at much greater risk for being overweight, becoming insulin resistant and developing cardiovascular disease because their master and peripheral clocks are likely to be out of sync.

Research in mice has shown that if they consume a high-fat meal at the end of their active period (the equivalent of a high-fat dinner for humans) they gain more weight, develop insulin resistance and have impaired cardiac function compared to mice that eat the same high-fat meal at the beginning of their active phase (breakfast).

Studies in people suggest that eating meals late in the day is linked to negative health effects, but a direct relationship has not been shown. Nevertheless, if when you eat is just as important as what you eat, it might not hurt to eat your larger meals earlier in the day if you can.


John Chatham

John Chatham, DPhil, is a professor of pathology and director of the Division of Molecular and Cellular Pathology at the University of Alabama at Birmingham.

Are You at Risk for Type 2 Diabetes?

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During American Diabetes Month in November, you may notice more people are talking about diabetes, a disease that affects 29 million Americans. It’s a great time to learn more about diabetes and the ways that you can decrease or manage your risk of developing the disease.

Diabetes mellitus is a problem with how your body handles blood glucose (sugar). People who have type 2 diabetes aren’t able to use the hormone insulin properly to remove glucose from the bloodstream for use in the fat and muscle cells.  Ultimately, this causes people with type 2 diabetes to have higher than normal levels of glucose in their blood.

You may have heard that someone who is overweight and has a large, apple-shaped body is more likely to develop metabolic syndrome—a group of health conditions such as elevated blood pressure, blood sugar and cholesterol levels—which may increase the risk of developing diabetes.  However, there are a number of less well known risk factors for type 2 diabetes including:

Some research even links non-health-related factors such as job security to an increased diabetes risk. A recent study published in the Canadian Medical Association Journal  analyzed data from 19 different studies including almost 141,000 participants which suggested that job insecurity was associated with a modest increased risk of diabetes.  Job insecurity has also been associated with weight gain (a diabetes risk factor) and coronary artery disease (a complication of diabetes).

Recognizing risk factors for diabetes and dealing with them, if possible, is important for both children and adults. Consuming a healthy, nutrient-rich diet and staying physically active can help maintain weight, manage stress and avoid type 2 diabetes and its many related complications. To learn more about ways to prevent diabetes, visit the American Diabetes Association website.


Barb Goodman, PhD, is a professor of physiology at the University of South Dakota.

Depression + Pregnancy = Diabetes?

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Morning sickness, swollen ankles and a growing belly are just a few of the many physiological changes that women experience during pregnancy. The changes  we can see are just the tip of the iceberg. Blood volume, bones, heart rate, skin and many other parts of a woman’s body function differently during pregnancy.

Pregnancy-related changes can sometimes lead to more serious health consequences for mother and baby during pregnancy and beyond. For example, gestational diabetes—a temporary condition in which the body can’t process sugar during pregnancy the way it usually does—can lead to a higher risk of other pregnancy complications, including having a large baby and increased chances of developing diabetes mellitus down the road. Now researchers have found a link between gestational diabetes and depression during pregnancy, a condition which affects an estimated 13 percent of moms-to-be.

A recent study showed that women who had more symptoms of depression in the first and second trimesters were at the greatest risk of developing gestational diabetes. The study also found that women who had gestational diabetes were four times more likely to develop postpartum depression after giving birth. Researchers say the relationship between the two conditions needs more study, but they think that the chemical changes in the brain that occur with depression during pregnancy may affect how we break down sugar.

These links emphasize the need to tune in to emotional shifts that many pregnant women experience. When crying jags and lack of energy lasts for more than two weeks or if symptoms get increasingly worse, it may be more than just pregnancy hormones at work. Women should also look out for the physical symptoms of depression which may include:

  • headaches
  • general aches and pains
  • stomach problems
  • loss of appetite (which may sometimes be mistaken for a side effect of morning sickness)

Now that doctors are learning more about the link between depression and gestational diabetes, they can monitor their patients more closely for both conditions during pregnancy. For more information about depression during and after pregnancy, visit the federal Office on Women’s Health website.

Erica Roth



What Blood Vessels Tell Us about Childhood Obesity

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Did you know that blood vessels can “talk?” That’s right: Changes in the cells within blood vessels can communicate important information about the overall health of the cardiovascular system. The inside of blood vessels are lined endothelial cells—protective cells that form a tight barrier through which only certain substances such as water or glucose can enter. Endothelial cells also make many substances that keep the vessels healthy so that the heart can effectively pump blood to all of the tissues and organs. While strong, endothelial cells are also sensitive to changes or inflammation within the body. So, if the cells become damaged or stop functioning properly, it can indicate that there is a problem occurring elsewhere in the body.

Tuning in to the messages that blood vessels can reveal what’s going on inside our bodies, not just what’s happening within the vessels themselves.  For example, vessels can expose the effects of obesity and can help scientists discover links between body composition and the body’s response to food and sugar intake.

In a recent study published in the Journal of Pediatrics, researchers measured the endothelial function of teens ages 12–19 years for clues into the relationship between obesity and how the body handled sugar. By conducting the study in teenagers with a wide range of body compositions—from normal weight to obese—they were able to make conclusions about blood vessel health, how it relates to obesity, and how obesity contributes to the development of problems in the body’s ability to handle sugar properly. They found that obese young people had higher levels of endothelial cell damage that correlated with the body’s inability to handle sugar. Indeed, in this example, the endothelial cells in the vessels “spoke” to the researchers about the health of the study participants.

This study also underscores the importance of preventing childhood obesity, which has been linked to a reduction in the body’s ability to regulate the amount of sugar in the blood. Limiting the intake of processed, high-sugar food and drinks is a great start. The second step is to increase physical activity during childhood and adolescent years. These habits, when started early, may carry into adulthood and lead to a healthier life. September is Childhood Obesity Awareness Month. Find more tips for helping kids maintain a healthy weight on the CDC website.

Audrey Vasauskas

How Your Immune System Can Make You Sick

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Your immune system has a Dr. Jekyll and Mr. Hyde complex when it comes keeping you healthy.  Traditionally, the immune system is seen as a good guy that kills off viruses and eats up bacteria attacking your body. However, it can also turn against you and cause disease.

To fight infection, the cells of your immune system produce proteins called cytokines that cause the infected area to swell, turn red, heat up and hurt. This reaction is called inflammation, and it helps you recover from viral and bacterial invaders relatively quickly.

Cytokines can also reduce inflammation, allowing for a system of checks and balances that prevents inflammation from lasting too long and hurting you instead of helping you. For example, the immune cell called “natural killer T cell” produces cytokines that cause inflammation and is kept in check by the immune cell “regulatory T cell”, which produces cytokines that counteract inflammation. Some immune cells can even produce both types of cytokines and switch roles. The immune cell “macrophage” can go from causing inflammation to kill the infection to preventing inflammation to help the injury heal.

Inflammation becomes bad when it lasts too long or is turned on at the wrong time. The cytokines can cause changes to your body that lead to disease, including stroke, heart disease, obesity and diabetes. Scientists are still unsure why the immune system can ignore its own safeguard. For obesity and diabetes, scientists at Harvard Medical School think the culprit is a hormone called leptin.

The researchers noticed that in obese people and obese mice immune cells found in fat called “mast cells” had five times more leptin than their lean counterparts. Moreover, mice that did not have leptin in their mast cells did not become obese or diabetic when put on a high-fat diet. Interestingly, obese mice lost weight and improved blood sugar levels when they were injected with mast cells with no leptin. This happened because mast cells with no leptin produced inflammation-reducing cytokines, while mast cells with leptin produced inflammation-causing cytokines, the research team said. In obesity and diabetes, leptin turned the immune system into a bad guy.

This is the first study to show that simply reducing the amount of leptin in mast cells can prevent, and even reverse, obesity and diabetes caused by a high-fat diet. Understanding the details of how our immune system causes disease can lead to new and better treatments to help people stay healthy.

Dao Ho, PhD


Dao H. Ho, PhD, is a biomedical research physiologist at Tripler Army Medical Center.

Look to the Sky for Lessons in High Blood Sugar

Karen SweazeaSo much of what we hear in health news today involves how what we eat or how much we move affects the way we live. For example, if we overeat sugar or unhealthy foods and don’t get enough exercise, we can find ourselves at increased risk for diabetes and cardiovascular disease. These can affect our quality of life or even shorten our lifespan.

As a comparative physiologist, I compare examples of animals and humans, how their diets affect their health and the factors that drive the development of cardiovascular disease with poor nutrition and diabetes.

I find birds to be the most interesting natural animal model of living successfully with high blood sugar. These amazing animals have blood sugar levels that are 1.5–2 times higher than the amount measured in mammals of similar body size, yet they display none of the typical characteristics that we associate with diabetes. This is because living with high blood sugar is just a normal part of their physiology. Another surprising fact: Unlike endurance athletes, who rely on sugar stores to power exercise, birds use fat to power flight. This is contrary to what people often assume.

Birds also defy the “rate of living theory of aging.” This theory suggests that animals with higher metabolisms (such as mice) do not live as long as those with low metabolisms (such as sloths). But birds go against this theory because they have very high metabolisms and are known to live relatively long lives.

We’ve still got a lot to learn about human health and disease from our fine, feathered friends and many other animals, too! To learn more about comparative physiology, check out the APS Dr. Dolittle blog.

Karen Sweazea, PhD, is an associate professor in the School of Nutrition & Health Promotion and the School of Life Sciences at Arizona State University.