Last month we began our discussion about insulin and discussed its role in car-bohydrate and protein metabolism. Now I will discuss how insulin affects fat me-tabolism and fuel selection, and dietary strategies for optimal insulin control. As mentioned last month, insulin causes cells to absorb glucose and use glucose as an energy source . This auto-matically decreases fatty acid oxidation, since more glucose is being used. Insu-lin thus switches your metabolism to a carbohydrate-burning mode. Insulin also promotes fatty acid synthesis by the liver. These fats are then transported through the blood for storage in fat cells. Not only does insulin stimulate the liver to synthe-size fat, but it also promotes fat uptake and storage by fat cells. Insulin stimulates glucose uptake by liv-er cells. After the glucose concentration builds up and glycogen stores become saturated, the remainder of the glucose is available for conversion to fat. This is one key reason why we recommend you divide your daily allotment of calories into several small meals instead of fewer large meals. This will present your liver with less carbohydrate load at a time, thus minimizing conversion to fat.
Fur-thermore, some intermediates of glucose metabolism generated by the citric acid cycle (the metabolic pathway responsible for the conversion of glucose to energy) activate the enzyme acetyl-CoA carboxyl-ase . This enzyme catalyzes the rate-limit-ing step in fatty acid biosynthesis. Simply put, if glucose concentrations build up too high in liver cells, this activates the enzy-matic pathway that converts glucose into fat. The newly synthesized fatty acids are coupled to glycerol to form triglycerides, the usual form in which fat is transported and stored . The triglycerides are then carried through the blood to fat cells in adipose depots. However, before they can be taken up by fat cells the fatty acids are cleaved from the glycerol by an enzyme called lipoprotein lipase . This enzyme is activated by insulin. Then the free fatty acids enter the fat cell and are combined with glycerol to reform the triglycerides. So, we see that insulin stimulates the rate-limiting steps of both fat synthesis and fat storage .
Not only does insulin act to promote storage of fat, it also inhibits the release of fatty acids from fat cells. The most po-tent stimuli for release of fatty acids from adipocytes (fat cells) are epinephrine and norepinephrine. Epinephrine, also known as adrenaline, is a hormone released from the adrenal gland in response to exercise, stress or fear. Norepinephrine is closely related, but is more commonly consid-ered a neurotransmitter than a hormone . It is released from nerve endings of the sympathetic nervous system, and is also activated by stress and exercise. Epi-nephrine and norepinephrine both work by activating an enzyme called hormone sensitive lipase. This enzyme splits the triglycerides into free fatty acids so they can be released from the fat cells. Insulin inhibits this enzyme, thereby preventing the breakdown of triglycerides and re-lease of fatty acids from fat cells. Finally, insulin also stimulates glucose uptake by fat cells. Once inside, the glucose is metabolized and forms alpha-glycerol phosphate. This is converted to glycerol, which is combined with fatty acids to form triglycerides.
This is an-other way in which insulin promotes fat storage . As you might expect, when insulin lev-els are low these effects are reversed. Low insulin levels, as occur between meals, during fasting and during exercise, take the brakes off fat metabolism. This al-lows hormone sensitive lipase to become active, which releases large quantities of fatty acids and glycerol into the blood. Then it is transported to muscles for use as fuel. Thus, in the absence of insulin, your body switches from burning mainly carbs to burning mostly fat. There are a couple of obvious implications here. One is that you don’t want to eat right before exercise if your goal is fat loss. This is especially relevant regarding your aerobic exercise. If you don’t eat for two hours before your aerobics, then insulin and blood glucose levels will be low so you’ll rely more heavily on fat as a fuel source. This is also why we recommend doing your aerobics first thing in the morning on an empty stomach. Also, it does make some sense to reduce carbohydrate intake when you’re trying to lose fat.
This “low-carb” approach helps lower insulin levels, thereby promoting use of fat as fuel. You don’t want to cut calories too severely, however, or this will reduce metabolic rate and promote muscle catabolism. So it would be nice if we had some other energy source to use in place of carbs. That’s where CapTri® fits in. It supplies a source of energy, which you can use in place of carbohydrates, to lower insulin and encourage the use of body fat for energy. CapTri® has a high thermogenic (heat producing) effect, which increases metabolic rate. Also, it is preferentially metabolized for energy and is not stored as body fat, in stark contrast to conven-tional fats. In summary, insulin promotes fat syn-thesis and storage and inhibits fat utili-zation. Therefore, we want to optimize insulin levels to maximize use of fat as fuel and minimize stored bodyfat. We’ll talk more about how to do that later. Insulin acts to promote utilization of car-bohydrate as fuel and inhibits the use of fat. Low insulin levels switches the fuel source oxidized from carbohydrate to fat. And since the blood glucose level de-termines the insulin level, we can see that the composition of the fuel mix oxidized (carbs versus fat) is determined primarily by the blood glucose concentration. If blood glucose is high, you’ll burn mostly carbs and not much fat.
If blood glucose is low, you’ll burn mostly fat. So you gen-erally want to keep blood glucose low to minimize bodyfat. That doesn’t mean you have to eat a low-carb diet, but you need to select your carbs carefully and always combine them with protein. Eating small, frequent meals helps. The most potent stimulus for insulin secretion is carbohydrate ingestion, espe-cially simple sugars . The rapid increase in blood glucose concentration causes a rapid insulin response. Normal blood glucose levels are around 90 mg/dl and basal (background) insulin secretion is minimal. After a meal when the blood glucose level rises above 100 insulin secretion is stimulated within three to five minutes. If blood glucose reaches about twice its normal value, insulin may increase to 10 times its normal level. This is accomplished through a combination of dumping insulin from the pancreas plus synthesis and release of insulin by the beta cells, which are the cells of the pancreas that make insulin.
The increased insulin level quickly reduces the glucose level by stimulating cells to absorb glu-cose. Then the insulin level decreases again just as rapidly as it increased. This constitutes an important feedback mecha-nism to maintain glucose control . Protein also stimulates insulin release, but not as strongly as carbohydrate. In-sulin acts to help transport some amino acids inside cells, especially the BCAAs (branched chain amino acids). It also stimulates the incorporation of amino acids into protein, as we discussed last month . Although I generally recommend that you consume carbohydrate and protein together, there is one exception. If you’re dieting to lose fat sometimes it works very well to have a protein drink before bed. This takes the edge off your appetite and helps you resist cheating . Also, this protein helps prevent muscle breakdown overnight and helps you burn fat while you’re sleeping. Right after a workout I would combine protein and carbs in about a 50:50 ratio. This will help replete glycogen stores and supply amino acids for growth. So the best supplement after workouts is 50/50 Plus™ which will sup-ply nutrients optimal to support growth and recovery.
The best supplement before bed is two scoops of Optimized Whey Protein™ to suppress muscle breakdown without inhibiting fat metabolism over-night. If you wake up starving in the middle of the night and have bad crav-ings, have another scoop of Optimized Whey Protein™. The best supplement to support your metabolism during low carb diets is CapTri®. Even during low-carb diets, a good rule of thumb is not to go below one gram per pound of body weight carbohydrate. Going too low in carbs promotes muscle breakdown and reduces thyroid hormone level, decreas-ing metabolic rate and fat metabolism. The exception might be if you’re carb loading for a contest, you might go lower than this for one or two days during the depletion phase . Some hormones released from the gas-trointestinal tract also stimulate insulin secretion. These are gastric inhibitory peptide, gastrin, secretin, and cholecys-tokinin. The intestinal tract releases these hormones after you eat a meal. Further-more, the autonomic nervous system can also stimulate the pancreas to release insulin . So we see that while insulin is neces-sary for growth, since it is responsible for transporting glucose and amino acids inside cells, too much insulin is not a good thing. Too much will result in fat accumulation. We have found that what works best is a relatively uniform blood glucose and insulin level, and fairly fre-quent feedings, including protein. This re-sults in the muscle cells being constantly bathed in the nutrients they need to grow and having enough insulin to stimulate amino acid uptake and protein synthesis, but not so much as to promote fat storage.
To achieve this you should eat every two and a half to three hours or so, which will work out to five or six meals a day. For most people, it works quite well to have, for the last meal of the day, Optimized Whey Protein™ right before bed, two to four scoops depending on your size. Seri-ous bodybuilders will want to use 50/50 Plus™ within 15 minutes after a workout, again two to four scoops. Whether or not you count this as a meal just depends on how many calories you need. Other meals should contain a protein source, a starch and a fibrous vegetable. The protein and the fiber slow the release of glucose from the starch, which serves as your primary glucose source. Pick your starch carefully. The best ones for bodybuilders are beans, rice, potatoes, sweet potatoes, corn, peas, lentils, whole grains, oatmeal, and so on. Refer to the Parrillo Performance Nutrition Manual for a detailed list of choices, including their nutrient profile. “Meal patterning” refers to eating small, frequent meals, every three hours or so. Most people do best to limit each meal to 500-600 calories. If you eat too many calories at a single meal this will elevate blood glucose, and thus more insulin than is desirable.
It will overwhelm the liver’s storage capacity for glycogen and result in “spilling over,” which refers to the conversion of carbohydrate into fat by the liver. “Meal structuring” refers to the design of each individual meal. As dis-cussed above, each meal should contain a protein source, a starch and a fibrous vegetable. Exactly how to combine these optimally varies from person to person. A good starting place is to consume one gram of protein per pound of body weight each day, and divide this evenly over six meals. Limit conventional fat to five-10 percent of total calories. The remainder of your calories are derived from carbo-hydrate . Try to maintain this structure at each meal, except the last one right before bed, in which a protein drink works well. Some people find they do better on even more protein, as much as two grams per pound of body weight per day. These are people who are training very, very hard, people who are dieting severely and in-dividuals who genetically store fat easily and find it hard to get lean. If you have a genetic predisposition toward carry-ing too much fat, you will find that you get leaner if you eat more protein and less carbohydrate.
Conversely, if you’re naturally thin and find it hard to put on muscle, you’ll do better with more carbs. The macronutrient ratio for each meal might vary from 30 percent protein, 60 percent carbohydrates and 10 percent fat to a 45 percent protein, 45 percent carbs and 10 percent fat. A 2:1 ratio of carbs to protein works better in naturally thin people because this results in a higher insulin level, promoting weight gain. The 1:1 carb to protein ratio works better for individuals who store fat easily, since it results in a lower insulin level. So far we have discussed food selection (refer to the Parrillo Nutrition Manual for a lot more details about this), meal patterning and meal structuring. We have mentioned a useful technique to maxi-mize fat burning: do your aerobics before breakfast and wait for two hours after a meal before working out. Another trick is to eliminate carbs from your last meal of the day (an Optimized Whey Protein™ shake before bed). Finally, another very effective way to reduce insulin levels is to substitute CapTri® for some of your starch. This will reduce the carbohydrate load and decrease insulin release, helping promote fat burning.
The way to use Cap-Controlling Insulin for Optimal Results, Part IITri® to help you lose weight is to use it in place of starch. The way to use it to help you gain weight is simply to add it to your regular meals to increase calories . The advantage of using CapTri® in this way is that it has very little tendency to convert to bodyfat. If your goal is to lose fat and gain muscle at the same time, you will need to train very intensely, and fairly fre-quently, and do your aerobics. The most effective supplement combination for this would be 50/50 Plus™ after workouts, Optimized Whey Protein™ before bed, CapTri® in place of some of your starch (maybe one tablespoon with each food meal, in place of 115 calories of starch), and creatine once a day (best taken with the 50/50 Plus™ after your workout). The Parrillo Performance Nutrition Manual has a lot more information about the details of meal patterning, meal struc-turing and food selection than I can fit in this article, but these are some of the key concepts in achieving your physique goals .
1. For more information about the physi-ologic effects of insulin, refer to Guyton AC and Hall JE. Textbook of Medical Physiology. W.B. Saunders Company, Philadelphia, 1996.
2. For detailed information about how to construct your diet for optimal insulin control, refer to the Parrillo Performance Nutrition Manual.