Exercise and blood glucose levels: Insulin and glucose responses to exercise

The notion that exercise reduces blood glucose levels is widespread. That notion is largely incorrect. Exercise appears to have a positive effect on insulin sensitivity in the long term, but also increases blood glucose levels in the short term. That is, exercise, while it is happening, leads to an increase in circulating blood glucose. In normoglycemic individuals, that increase is fairly small compared to the increase caused by consumption of carbohydrate-rich foods, particularly foods rich in refined carbohydrates and sugars.

The figure below, from the excellent book by Wilmore and colleagues (2007), shows the variation of blood insulin and glucose in response to an endurance exercise session. The exercise session’s intensity was at 65 to 70 percent of the individuals’ maximal capacity (i.e., their VO2 max). The session lasted 180 minutes, or 3 hours. The full reference to the book by Wilmore and colleagues is at the end of this post.

As you can see, blood insulin levels decreased markedly in response to the exercise bout, in an exponential decay fashion. Blood glucose increased quickly, from about 5.1 mmol/l (91.8 mg/dl) to 5.4 mmol/l (97.2 mg/dl), before dropping again. Note that blood glucose levels remained somewhat elevated throughout the exercise session. But, still, the elevation was fairly small in the participants, which were all normoglycemic. A couple of bagels would easily induce a rise to 160 mg/dl in about 45 minutes in those individuals, and a much larger “area under the curve” glucose response than exercise.

So what is going on here? Shouldn’t glucose levels go down, since muscle is using glucose for energy?

No, because the human body is much more “concerned” with keeping blood glucose levels high enough to support those cells that absolutely need glucose, such as brain and red blood cells. During exercise, the brain will derive part of its energy from ketones, but will still need glucose to function properly. In fact, that need is critical for survival, and may be seen as a bit of an evolutionary flaw. Hypoglycemia, if maintained for too long, will lead to seizures, coma, and death.

Muscle tissue will increase its uptake of free fatty acids and ketones during exercise, to spare glucose for the brain. And muscle tissue will also consume glucose, in part for glycogenesis; that is, for making muscle glycogen, which is being depleted by exercise. In this sense, we can say that muscle tissue is becoming somewhat insulin resistant, because it is using more free fatty acids and ketones for energy, and thus less glucose. Another way of looking at this, however, which is favored by Wilmore and colleagues (2007), is that muscle tissue is becoming more insulin sensitive, because it is still taking up glucose, even though insulin levels are dropping.

Truth be told, the discussion in the paragraph above is mostly academic, because muscle tissue can take up glucose without insulin. Insulin is a hormone that allows the pancreas, its secreting organ, to communicate with two main organs – the liver and body fat. (Yes, body fat can be seen as an “organ”, since it has a number of endocrine functions.) Insulin signals to the liver that it is time to take up blood glucose and either make glycogen (to be stored in the liver) or fat with it (secreting that fat in VLDL particles). Insulin signals to body fat that it is time to take up blood glucose and fat (e.g., packaged in chylomicrons) and make more body fat with it. Low insulin levels, during exercise, will do the opposite, leading to low glucose uptake by the liver and an increase in body fat catabolism.

Resistance exercise (e.g., weight training) induces much higher glucose levels than endurance exercise; and this happens even when one has fasted for 20 hours before the exercise session. The reason is that resistance exercise leads to the conversion of muscle glycogen into energy, releasing lactate in the process. Lactate is in turn used by muscle tissues as a source of energy, helping spare glycogen. It is also used by the liver for production of glucose through gluconeogenesis, which significantly elevates blood glucose levels. That hepatic glucose is then used by muscle tissues to replenish their depleted glycogen stores. This is known as the Cori cycle.

Exercise seems to lead, in the long term, to insulin sensitivity; but through a fairly complex and longitudinal process that involves the interaction of many hormones. One of the mechanisms may be an overall reduction in insulin levels, leading to increased insulin sensitivity as a compensatory adaptation. In the short term, particularly while it is being conducted, exercise nearly always increases blood glucose levels. Even in the first few months after the beginning of an exercise program, blood glucose levels may increase. If a person who was on a low carbohydrate diet started a 3-month exercise program, it is quite possible that the person’s average blood glucose would go up a bit. If low carbohydrate dieting began together with the exercise program, then average blood glucose might drop significantly, because of the acute effect of this type of dieting on average blood glucose.

Still exercise is health-promoting. The combination of the long- and short-term effects of exercise appears to lead to an overall slowing down of the progression of insulin resistance with age. This is a good thing.

Reference:

Wilmore, J.H., Costill, D.L., & Kenney, W.L. (2007). Physiology of sport and exercise. Champaign, IL: Human Kinetics.

Compensatory adaptation as a unifying concept: Understanding how we respond to diet and lifestyle changes

Trying to understand each body response to each diet and lifestyle change, individually, is certainly a losing battle. It is a bit like the various attempts to classify organisms that occurred prior to solid knowledge about common descent. Darwin’s theory of evolution is a theory of common descent that makes classification of organisms a much easier and logical task.

Compensatory adaptation (CA) is a broad theoretical framework that hopefully can help us better understand responses to diet and lifestyle changes. CA is a very broad idea, and it has applications at many levels. I have discussed CA in the context of human behavior in general (Kock, 2002), and human behavior toward communication technologies (Kock, 2001; 2005; 2007). Full references and links are at the end of this post.

CA is all about time-dependent adaptation in response to stimuli facing an organism. The stimuli may be in the form of obstacles. From a general human behavior perspective, CA seems to be at the source of many success stories. A few are discussed in the Kock (2002) book; the cases of Helen Keller and Stephen Hawking are among them.

People who have to face serious obstacles sometimes develop remarkable adaptations that make them rather unique individuals. Hawking developed remarkable mental visualization abilities, which seem to be related to some of his most important cosmological discoveries. Keller could recognize an approaching person based on floor vibrations, even though she was blind and deaf. Both achieved remarkable professional success, perhaps not as much in spite but because of their disabilities.

From a diet and lifestyle perspective, CA allows us to make one key prediction. The prediction is that compensatory body responses to diet and lifestyle changes will occur, and they will be aimed at maximizing reproductive success, but with a twist – it’s reproductive success in our evolutionary past! We are stuck with those adaptations, even though we live in modern environments that differ in many respects from the environments where our ancestors lived.

Note that what CA generally tries to maximize is reproductive success, not survival success. From an evolutionary perspective, if an organism generates 30 offspring in a lifetime of 2 years, that organism is more successful in terms of spreading its genes than another that generates 5 offspring in a lifetime of 200 years. This is true as long as the offspring survive to reproductive maturity, which is why extended survival is selected for in some species.

We live longer than chimpanzees in part because our ancestors were “good fathers and mothers”, taking care of their children, who were vulnerable. If our ancestors were not as caring or their children not as vulnerable, maybe this blog would have posts on how to control blood glucose levels to live beyond the ripe old age of 50!

The CA prediction related to responses aimed at maximizing reproductive success is a straightforward enough prediction. The difficult part is to understand how CA works in specific contexts (e.g., Paleolithic dieting, low carbohydrate dieting, calorie restriction), and what we can do to take advantage (or work around) CA mechanisms. For that we need a good understanding of evolution, some common sense, and also good empirical research.

One thing we can say with some degree of certainty is that CA leads to short-term and long-term responses, and that those are likely to be different from one another. The reason is that a particular diet and lifestyle change affected the reproductive success of our Paleolithic ancestors in different ways, depending on whether it was a short-term or long-term change. The same is true for CA responses at different stages of one’s life, such as adolescence and middle age; they are also different.

This is the main reason why many diets that work very well in the beginning (e.g., first months) frequently cease to work as well after a while (e.g., a year).

Also, CA leads to psychological responses, which is one of the key reasons why most diets fail. Without a change in mindset, more often than not one tends to return to old habits. Hunger is not only a physiological response; it is also a psychological response, and the psychological part can be a lot stronger than the physiological one.

It is because of CA that a one-month moderately severe calorie restriction period (e.g., 30% below basal metabolic rate) will lead to significant body fat loss, as the body produces hormonal responses to several stimuli (e.g., glycogen depletion) in a compensatory way, but still “assuming” that liberal amounts of food will soon be available. Do that for one year and the body will respond differently, “assuming” that food scarcity is no longer short-term and thus that it requires different, and possibly more drastic, responses.

Among other things, prolonged severe calorie restriction will lead to a significant decrease in metabolism, loss of libido, loss of morale, and physical as well as mental fatigue. It will make the body hold on to its fat reserves a lot more greedily, and induce a number of psychological responses to force us to devour anything in sight. In several people it will induce psychosis. The results of prolonged starvation experiments, such as the Biosphere 2 experiments, are very instructive in this respect.

It is because of CA that resistance exercise leads to muscle gain. Muscle gain is actually a body’s response to reasonable levels of anaerobic exercise. The exercise itself leads to muscle damage, and short-term muscle loss. The gain comes after the exercise, in the following hours and days (and with proper nutrition), as the body tries to repair the muscle damage. Here the body “assumes” that the level of exertion that caused it will continue in the near future.

If you increase the effort (by increasing resistance or repetitions, within a certain range) at each workout session, the body will be constantly adapting, up to a limit. If there is no increase, adaptation will stop; it will even regress if exercise stops altogether. Do too much resistance training (e.g., multiple workout sessions everyday), and the body will react differently. Among other things, it will create deterrents in the form of pain (through inflammation), physical and mental fatigue, and even psychological aversion to resistance exercise.

CA processes have a powerful effect on one’s body, and even on one’s mind!

References:

Kock, N. (2001). Compensatory Adaptation to a Lean Medium: An Action Research Investigation of Electronic Communication in Process Improvement Groups. IEEE Transactions on Professional Communication, 44(4), 267-285.

Kock, N. (2002). Compensatory Adaptation: Understanding How Obstacles Can Lead to Success. Infinity Publishing, Haverford, PA. (Additional link.)

Kock, N. (2005). Compensatory adaptation to media obstacles: An experimental study of process redesign dyads. Information Resources Management Journal, 18(2), 41-67.

Kock, N. (2007). Media Naturalness and Compensatory Encoding: The Burden of Electronic Media Obstacles is on Senders. Decision Support Systems, 44(1), 175-187.

What about some offal? Boiled tripes in tomato sauce

Tripe dishes are made with the stomach of various ruminants. The most common type of tripe is beef tripe from cattle. Like many predators, our Paleolithic ancestors probably ate plenty of offal, likely including tripe. They certainly did not eat only muscle meat. It would have been a big waste to eat only muscle meat, particularly because animal organs and other non-muscle parts are very rich in vitamins and minerals.

The taste for tripe is an acquired one. Many national cuisines have traditional tripe dishes, including the French, Chinese, Portuguese, and Mexican cuisines – to name only a few. The tripe dish shown in the photo below was prepared following a simple recipe. Click on the photo to enlarge it.

Here is the recipe:

- Cut up about 2 lbs of tripe into rectangular strips. I suggest rectangles of about 5 by 1 inches.
- Boil the tripe strips in low heat for 5 hours.
- Drain the boiled tripe strips, and place them in a frying or sauce pan. You may use the same pan you used for boiling.
- Add a small amount of tomato sauce, enough to give the tripe strips color, but not to completely immerse them in the sauce. Add seasoning to taste. I suggest some salt, parsley, garlic powder, chili powder, black pepper, and cayenne pepper.
- Cook the tripe strips in tomato sauce for about 15 minutes.

Cooked tripe has a strong, characteristic smell, which will fill your kitchen as you boil it for 5 hours. Not many people will be able to eat many tripe strips at once, so perhaps this should not be the main dish of a dinner with friends. I personally can only eat about 5 strips at a time. I know folks who can eat a whole pan full of tripe strips, like the one shown on the photo in this post. But these folks are not many.

In terms of nutrition, 100 g of tripe prepared in this way will have approximately 12 g of protein, 4 g of fat, 157 g of cholesterol, and 2 g of carbohydrates. You will also be getting a reasonable amount of vitamin B12, zinc, and selenium.

The Comics: A Funny Place to Find Serious Public Health Issues?

On a recent trip to visit my in-laws, I was very happy to find that I had time to relax and read the paper in the morning. For me, the joy is found in reading the comics and completing the word search. So you can imagine my surprise when I sat down to read the comics and found that Doonesbury was discussing a very serious public health issue- sexual assault and harassment in the military. Apparently this storyline has been playing itself out in a series that follows Roz (a female soldier who is worried and seeking help for her friend Melissa). Melissa is being reassigned so that a superior officer can "prey" on her.

According to the Veterans Administration (VA) website, "Both women and men can experience sexual harassment or sexual assault during their military service. VA refers to these experiences as military sexual trauma, or MST". Like other types of trauma, MST can negatively impact a person's mental and physical health, even many years later. Every VA facility has a designated MST Coordinator who serves as a contact person for MST-related issues. Here I'll give a shout out to my favorite public health social worker, Micaela Cohen, who is the field and program development coordinator for the national military sexual trauma program at the VA.

Obviously, sexual assault is a serious public health issue, as it can put soldiers and veterans at a higher risk for negative health effects, such as depression. MST can also affect the rate at which health services are utilized. A recent study published in the journal Women's Health Issues reported that, "the under utilization of specialized PTSD services by younger women could be due, in part, to the fact that a significant proportion of PTSD in female veterans is associated with a history of military sexual abuse. Women with a history of military sexual trauma may not feel comfortable either in mixed-gender groups or using services in which treatment is oriented primarily toward combat-related PTSD."

For years, Doonesbury's author- Garry Trudeau, has been taking these types of statistics and important global issues and using them to shape his comic strip. For example, in 2006, he had his character B.D. wounded as he served in Iraq. In a 2007 interview with Military.com about the storyline, Mr. Trudeau stated, "I originally considered having him die in combat, but I concluded that while that might have caused a brief sensation, it would soon be forgotten. In the alternative, by giving B.D. a life-altering wound, I could set in motion a sustained story arc that tracked the arduous recovery and readjustment issues that a survivor might expect to face. "

Although public health practitioners may come across stories and statistics about the health issues and challenges faced by our service members everyday...the general population does not. And even if they do, I'm not sure that they would feel comfortable talking about it. Therefore, I think that inserting public health and social justice issues into the comics is an innovative idea. The comics are a "familiar" section in the newspaper to readers of all ages. We get to know the characters and follow them for years or even decades. The characters can give us a shared and "safe" way to discuss difficult issues. I just hope that as newspapers continue to struggle and more of us are reading our news online...that we don't forget to read the comics! It might not always be a laugh...it might be something even more important.

iPads and other wireless technology: Forget the fun...will they be the next great public health invention?

iPad mania is sweeping the nation! It even made a cameo in my new favorite show, "Modern Family". In a recent episode, all Phil Dunphy wants for his birthday is an iPad. He is excited to use it for web browsing, eBook reading, and video watching. But what if it could also improve his health?
A great article in The Economist this week called, "When your carpet calls your doctor", examines how the convergence of wireless communications, social networking, and medicine will transform health care.

This concept appears quite realistic for several reasons:

• Doctors are already using and comfortable with the technology. The article quotes a forthcoming report by the California Health Care Foundation that found that two-thirds of doctors are already using "smart phones" (a mobile phone with advanced capabilities such as Internet connectivity). Doctors are also used to turning to their computers and/or wireless devices for programs like Epocrates to review treatment information and decision making tools.

• Wireless technology reduces treatment barriers such as the distance and/or availability of the health care provider. One example of the technology being developed is a device which will be able to contact a doctor when his/her elderly patient is about to take a fall in their residence. The article also quotes successful work being done in developing countries such as Rwanda and Peru. This work has expanded to public health programs in the United States, such as Text4baby. This is an educational program of the National Healthy Mothers, Healthy Babies Coalition (HMHB). Women who sign up for the service will receive free text messages each week, timed to their due date or baby's date of birth.

• This technology is aiming to address barriers and facilitators of Behavior Change, not just an increase in knowledge! The focus soley on education to increase knowledge is the downfall of many public health programs. Knowledge alone will not change behavior. However, check out the programs from the company Virgin HealthMiles. They have begun using online social networks, through which co-workers or family members can cheer on or nag patients electronically, in order to encourage exercise or weight loss. The company is beginning to explore how to increase the level of social support and social/family acceptance that patients receive regarding their recommended treatment. Lack of support in these areas can often be a barrier to treatment success.
  

Of course there are still a few things that remain to be seen about the success of these eHealth programs. What are the privacy implications? Are smart phones (or similar wireless technology) widely available to the populations that most need these interventions (e.g., low socioeconomic status, the elderly, rural residents, etc)? What do my readers think?

Personal Responsibility and Health: Who Should Pay For Your Cheeseburgers?

Last year one of my "friends" on Facebook posted a status that infuriated me. It said "Why should I pay for health care for people who can't stop eating cheeseburgers from McDonald's?" I'm never one to downplay the importance of individual health behaviors like diet and exercise. In the three years since I met my husband he has gone from eating "less than one" (his words) serving of fruits/vegetables a day to at least four or five a day. And I'm sure that was the result of my gentle "nudging" because I was concerned for his health. However, this oversimplification that all acute or chronic illnesses are caused by "overweight people eating McDonald's" is incredibly ignorant. We cannot have a discussion about facilitators and barriers to good health outcomes without considering a person's environment, economic status, profession, family, peers, attitudes, beliefs, knowledge, etc. The list goes on.

There was an interesting article in The New York Times this week, No Matter What, We Pay for Others' Bad Habits, that explores this very issue of personal responsibility. The story had legs on Facebook and Twitter, so I wanted to incorporate it into the blog. And because I follow such thoughtful and interesting people online, I thought I'd include one of their quotes to demonstrate my point above (I removed her name in case she isn't interested in being a blog celebrity):

• "The notion of personal responsibility becomes almost a moot point if we don't have an environment that supports our ability to responsibly make "the healthy choice". As the Institute of Medicine says, "It is unreasonable to expect that people will change their behavior easily when so many forces in the social, cultural, and physical environments conspire against such change".
  

Some thoughts:

• Perhaps the hourly worker would like to make it to his healthy/yearly check-up at the doctor. However, because his job doesn't offer sick time since he's part-time, he could be fired for missing work. Therefore, he decides to miss his appointment, flu shot, blood pressure check, etc....because his paycheck is more important to his family.
  

• Perhaps there are a large number of people in a lower socioeconomic bracket that eat McDonald's cheeseburgers (as my Facebook "friend" noted above)...but maybe that's because there are no Whole Foods or Trader Joe's Markets in their neighborhoods. And maybe they don't have a car to drive to one and/or the bus route doesn't pass those stores. And I know that those $1 burgers are a little less expensive than the $10 Rotisserie chicken that Whole Foods sells.

• Perhaps a parent wants their child to walk or ride their bike to school for exercise, but their neighborhood isn't safe. What if there are no side walks?
  

• And what about the impact of genetic and environmental factors in disease? A strong family history of cancer and heart disease cannot always be canceled out by eating vegetables and heading to the gym. And what about those people that are exposed to dangerous chemicals in their jobs. What about those that now suffer due to exposure to asbestos in their jobs before we knew how bad it was? Do they not deserve health care?
  

Again, I'm not downplaying personal responsibility. Patient compliance, healthy eating, and exercise are incredibly important. But let's not forget the complex systems which influence the health of individuals.

And to end with a Facebook "friend's" status that made me less angry: "I mean, seriously, if you're getting that angry cuz a fellow human being can now go to the 'effin doctor, you probably could use a few moments of self reflection..."

Talkin' Bout A Revolution...Jamie Oliver is much louder than a whisper!

So I just finished watching the premiere episode of "Jamie Oliver's Food Revolution". It is a new show on ABC that chronicles the journey of English chef Jamie Oliver as he tries to change the eating habits of residents in Huntington, West Virginia. Huntington was recently crowned the most unhealthy city in America.
It is obvious that Jamie has good intentions. He has left his family for several months to work on this project. He is especially concerned about the quality of food being served in the Huntington schools. However, my reaction to the first episode was "No, no, no! Stop what you're doing and talk to these people first!"

The most important part of any public health intervention is getting to know the community you are working with. The worst thing you can do is come in as an "outsider" and start barking orders. Some questions you should ask before getting started are: How does this community operate? Who makes the decisions? What are some of the barriers to serving fresh food in schools? What are the USDA guidelines? (which Jamie knows nothing about) Who are the individuals you want/need to get on board with your idea? How do the parents feel about their children's eating habits? How can you get their buy-in? What would be a realistic timeline for assessment/buy-in before trying to implement change?

Jamie went about this all backwards (which may very well have been to increase drama for a TV show, but it is still a great example of "what not to do"). His first day in town he was told he was viewed as an "outsider" by the trusted radio host...and still proceeded to go into the elementary school and lecture the chefs on how disgusting the food is (after only observing them for one day). And he's surprised he's getting push back on his efforts?! The only small victory he has is creating a partnership with "Pastor Steve" at the local Baptist church. Steve is a trusted leader in the community and knows the families and their challenges very well.

Too bad Jamie did not look to better models of this kind of community effort. Shape Up Somerville (Somerville, MA) began as a community based research study at Tufts University targeting 1^st through 3^rd graders in the Somerville Public Schools. Today there is Coordinator working on active and healthy living programs supported by the Health Department and a Taskforce that is a collaboration of over 11 initiatives and 25 stakeholders involved in working on various interventions across the city. Program components include a focus on the school lunch program, local restaurants, walk ability and safe routes to school, etc. (I'll give a shout out here to one of my public health heroes- Julia Bloom- who helped Tufts bring this model to more rural communities across the country!)

Shape Up Somerville represents a strong program that began with a strong base. The original program engaged key stakeholders and did not try to change the community without first finding out how it worked. The community and parent outreach were an obvious key to success...where that aspect is basically forgotten in the "Food Revolution". Jamie just seems like one man on a mission to change. At the end of the episode Jamie is visibly upset and says "they don't know why I'm here". Yeah- that's because you're an outsider lecturing them on how they should raise their kids!

I'll probably watch the second episode where he actually starts to engage the community...how about you?