Insulin is perhaps the most well known of all hormones and in the halls of health, fitness, and fat loss. It is mostly maligned and drastically misunderstood. As with many things in health and fitness there is more to the simple story told about insulin.
Insulin functions very much like your hands when you are eating. Just as it would be extremely difficult to eat without hands, insulin feeds the tissue of the body in the same way. Insulin is required to facilitate nutrient uptake in the cells. Without insulin, your cells would literally starve and die.
Insulin is made in the beta cells of the pancreas and is released into the blood stream in response to food. It assures these nutrients get into the cell. Insulin’s primary job is to make sure the cells have enough glucose, and therefore it has a strong impact on blood sugar levels.
In fact, glucose is the primary stimulator of insulin release. In response to food and/or stress, blood glucose levels will rise. Insulin is used to lower blood sugar and balance things back out.
Insulin works by increasing the amount of glucose receptors on the membranes of cells. So, when insulin interacts with cellular physiology it results in an increased ability for the cell to take in glucose.
When insulin is repeatedly secreted in large quantities, over time the cells become less sensitive to its message. This is analogous to walking into a room with a strong smell. When you first enter, you are acutely aware of the odor and may cover your nose in response. After several minutes however, the smell becomes diminished and you no longer smell it.
This is what happens to the cells when they become insulin resistant. They no longer respond to insulin the same way. This has consequences for cellular energy and health. When this happens, the cell does not get fed and blood sugar levels rise to dangerous levels.
The liver is an important player in the insulin story. Insulin signals the liver to increase its production of glycogen, the body’s source of stored sugar. It also suppresses the liver’s capacity to make new sugar, a process called gluconeogenesis. When the liver loses its ability to sense and respond to insulin this results in decreased sugar storage and an overproduction of glucose by the body.
This results in the body doing the only thing it can to balance things out, store all the extra sugar as fat. So long as the fat cells remain sensitive to insulin, the body can stay protected by storing all the sugar away for a rainy day.
It is important to understand that insulin resistant is not an all or nothing thing. Some tissues can remain sensitive to insulin while others lose their responsiveness. The muscle, fat, and liver all will have their own response to insulin.
In other words, you can remain sensitive in one tissue while being resistant in another. When the liver loses its ability to sense and respond to insulin, it creates the most problems for metabolic fat burning and health.
Insulin and stress
What many people don’t realize is that insulin is utilized even when sugar or carbs are not eaten. When the body is under stress, it will release stress hormones including adrenaline, noradrenaline, and cortisol whose chief functions are to raise blood sugar. This supplies energy to power the fight or flight response.
Historically this stress response was a chief means of survival. In modern times however, this ancient physiology can be damaging since rather than fighting or fleeing, we instead sit and seethe.
This causes large amounts of stored sugar to flood the blood stream and sit there. If the blood glucose is not used for activity, insulin has to be called on to adjust the blood sugar back to normal.
Insulin and stress hormones are not a great mix for the body. When this seesaw battle of stress hormone secretion and insulin release happens too frequently, the body begins to lose its metabolic sensitivity.
In other words, it begins to treat both these hormones like the boy who cried wolf and no longer responds to their signals. This is a key reason for insulin resistance.
This is perhaps the most insidious metabolic disturbance of the modern day. It plays a role in almost every major disease because of its strong impact on obesity. While many blame the hormone cortisol for storing belly fat, the combination of cortisol and insulin is the actual culprit.
Insulin and fat storage
Many people refer to insulin as the fat storing hormone, but it is important to understand where this comes from. Remember, insulin’s primary job is to lower blood sugar and get it into the cell where it can be used for energy.
Along with this, it also helps the cellular intake of amino acids and other nutrients. As we discussed, insulin resistance can result in large amounts of blood sugar that cannot be used.
At first glance, this may seem like a good thing. After all, if the body can’t use sugar well, then surely it will begin to use its fat stores? Unfortunately this is not how it works.
When confronted with excess food, insulin is released to get the nutrients into the cell to be burned. It also wants to save any leftover for a rainy day. So, it interacts with two key fat releasing and storing enzymes. These are lipoprotein lipase (LPL) and hormone sensitive lipase (HSL). This is where the fat storing action of insulin becomes prominent.
On your fat cells, LPL works to break down the triglyceride molecule (three fats attached to a glycerol backbone) to individual fats so they can be stored in the cell. HSL does the opposite, breaking down triglycerides in the cell so the fat can be released and burned.
Insulin is a powerful stimulator of LPL and a powerful inhibitor of HSL. So, as insulin levels rise in the body they not only increase fat storage, but perhaps more importantly block fat breakdown.
Just because fat gets released from a cell does not mean it will be burned. Insulin also has a role to play here. The chief rate limiting step in getting fat into a cell and burned has to do with an enzyme called CPT-1. Guess what insulin does to this enzyme? Blocks it!
Adding insult to injury, the liver is no longer responding to insulin’s suppressive effect on glucose production. This results in muscle protein being stripped and used for energy instead instead of fat. The body does this because it can easily convert the amino acids alanine and glutamine to sugar. Taken together, insulin resistance means fat storage and muscle loss.
Insulin and muscle building
Before we jump to conclusions and assume all insulin is bad, we need to take a step back. Insulin itself is not bad, it is insulin resistance that is the problem. Insulin is key to feeding our cells, and it is essential to get amino acids into tissues to provide fuel for muscle growth.
In other words, for body change you need enough insulin to build muscle, but not so much to store fat. Rather than simply trying to lower insulin to extremely low levels and possibly losing muscle in the process, it is far better to maximize insulin sensitivity.
The best way to maximize insulin sensitivity is through exercise. An August 2010 review in the American Journal of Physiology, Endocrinology and Metabolism points to muscle contraction as an insulin independent mechanism to move glucose into the cells.
Muscle contractions increase the number of glucose receptors on the cell surfaces. This is important because these receptors are down regulated in insulin resistance. Through contraction induced mechanisms the cell can get fed, increase its glycogen storage, and retain or even gain muscle.
Putting it together.
While a whole book could be written on insulin metabolism, hopefully you are getting the picture that lowering insulin is not as smart as maximizing insulin sensitivity. In fact, simply having low insulin levels does not guarantee you will remain insulin sensitive.
A 2006 study (volume 1 #1) in the Journal of Cardiometabolic Syndrome showed the amount of muscle on an individual determines 40% of his or her insulin sensitivity and 70-90% of blood glucose clearance. This means restoring insulin sensitivity has everything to do with using resistance training as the center point of an exercise plan.
And not just any resistance training will do. To develop full insulin sensitivity it requires heavy weights and more focused contractions. A study in the February 2008 issue of Cell Metabolism showed that growth of the faster twitch type IIb muscle fibers has the most benefit in insulin and blood sugar control.
The study showed activation of these fibers positively alters the expression of 800 or so genes responsible for insulin sensitivity. Only heavy and full fatigue resistance training and sprinting activates these fibers, aerobic exercise does not.
Combining the understanding of resistance training with a knowledge of how food impacts insulin allows adjustment of exercise and food timing. Manipulating these can allow tailored results for muscle gain and/or fat loss.
For those seeking fat loss, insulin needs to be managed differently. Obese individuals already have poor insulin sensitivity and very high resting insulin levels.
This means their bodies have a difficult time burning fat. For these types, any type of glucose (sugar or starch) should be minimized both pre and post workout.
The common belief that carbs should be consumed after the workout does not apply as strongly to those seeking fat loss. Instead, these types should time their carbohydrate intake at the most insulin sensitive times.
These times are in the morning after an overnight fast and then within 1 hour after a workout. However, the carbohydrate load should be smaller and lower on the glycemic index. Preworkout carbohydrate intake is not wise because it will raise insulin further and give the body sugar to burn instead of fat. Protein should be used here instead.
For those wanting to optimize muscle growth, carbohydrates should be eaten throughout the day. Small amounts can be taken 45 to 60 minutes before a workout and larger amounts should be taken after the workout. Good post workout choices are high glycemic index carbs like bananas, potatoes, and pasta.
For those wanting both muscle gain and fat loss a mix of the two is best. Limiting high starch meals to morning and post workout, but increasing the amounts and glycemic index of carbs in the post workout period will help build muscle without providing too much of a stimulus for fat storage.
One final caveat when managing insulin is dairy. Dairy foods are low glycemic index but are unique as a protein source because they stimulate insulin much more then their glycemic index would suggest.
This is a good thing for those seeking muscle gain and fat loss. Whey protein and other dairy proteins can be used to provide an insulin stimulus without the high sugar load. However, the recommendation to use things such as chocolate milk may push things more toward fat storage and may not be smart except for those wanting strictly muscle gain.
Understanding insulin is an essential part of the health, fitness, and fat loss lifestyle. Insulin can be both your best friend and worst enemy when it comes to fat loss or muscle building. Developing a smart insulin strategy can help unlock the full potential of the metabolism. There are other fat storing hormones (ASP, GIP-1, Ghrelin, Etc) but insulin is probably the most important