The Paleo Diet for Athletes (15 page)

TABLE 5.2

Blood Glucose and Insulin Responses (239-kcal sample)

The glycemic reference is white bread with a glucose and insulin response of 100.

Meat and seafood generally don’t contain any carbohydrate and cause minimal rises in blood sugar and insulin levels (see
Table 5.2
).

Surprising—and somewhat alarming—is the paradoxically high insulin response of milk (90) and fermented milk (98) compared with their low glycemic responses (30 and 15, respectively). A similar dissociation of the blood insulin and glucose response occurs in yogurt. Generally, however, the GI of most foods nicely parallels the insulin response or insulin index (II). Hence, high GI foods are almost always high II foods.

Because the carbohydrates in Paleolithic diets came from minimally processed wild plants, and because hunter-gatherers ate no refined grains or sugars (except for seasonal honey), the glycemic loads of their diets would have been very low by modern standards. But remember, the fat and protein intake would have been higher. What are the implications of these dietary macronutrient patterns upon endurance performance?

Muscle Fuel Sources

When you are at rest and not exercising, about 60 percent of the energy needed to fuel your body is provided by fats. The balance is provided by carbohydrate because protein is a relatively minor source of energy. When you are at rest, free fatty acids (FFA) circulating in the bloodstream provide the major source of fat to fuel metabolism. FFA in the blood comes from fat stored in cells in your belly, thighs, and any other place where you accumulate fat. At low exercise levels (25 percent of your aerobic capacity or max VO
₂
), fat provides 80 percent of the muscle’s
fuel, and the balance (about 20 percent) comes from carbohydrate. At 25 percent max VO
₂
, most of the fat fueling muscle contraction still comes from FFA in the blood, although a small amount is derived from stored fat droplets inside muscle cells—the intramuscular triglycerides (IMT). Twenty to 30 years ago, exercise scientists didn’t pay much attention to IMT when it came to endurance performance; their sights were narrowly focused upon glycogen. Glycogen is made up of chains of glucose molecules, which is how carbs are stored inside muscle cells.

Let’s continue with the tutorial on muscle fuel sources so you can eventually see how Paleolithic macronutrient patterns weren’t necessarily a liability for performance. As exercise intensity increases, so does IMT usage by the muscles. At approximately 65 percent max VO
₂
, IMT stores are being maximally drawn on, so that energy contribution from fats and carbs is about 50:50. When exercise intensity increases to 85 percent max VO
₂
, IMT supplies only 25 percent of the energy needed for muscle contraction. Finally, as you continue to 100 percent of your aerobic capacity, glucose from muscle glycogen stores becomes the preferred and necessary fuel source. Why is that? Why isn’t fat used to fuel very intense and high-level exercise?

If you look at the caloric density of fat, it has 9 calories per gram—more than twice as much as carbohydrate’s 4 calories per gram. So, at least on the surface, it looks like fat would be the preferred fuel for high-level exercise because it’s such a concentrated energy source. But there’s another side to the story, and it’s called fuel efficiency—a concept you know better as “miles per gallon.” When you look at body fuel efficiency in terms of oxygen rather than energy density, the picture changes. It takes considerably more oxygen for muscles to burn fat than to burn carbohydrate. Carbohydrate yields 5.05 calories per liter of oxygen, whereas fat gives only 4.69—a difference of 7 percent. During aerobic metabolism, this 7 percent caloric advantage for carbs translates into a threefold faster energy production in the muscles. The take-home message: Muscle stores of glycogen are absolutely essential in performing endurance exercise at or above 85 percent max VO
₂
for any extended period.

But here’s the problem: There is a limit to how much glycogen the muscles can store. Trained endurance athletes can store twice as much muscle glycogen as couch potatoes can. However, it’s important to know that muscle glycogen stockpiles cannot be shifted from one muscle to another during exercise: Any glycogen in your arms will not help your legs and vice versa. The values for muscle glycogen in
Table 5.3
represent whole-body muscle stores and obviously will be considerably lower for specific muscle groups.

TABLE 5.3

Total Body Carbohydrate Stores in a Nontrained Person

Because the muscle glycogen stores are limited, high-intensity endurance activity (> 85 percent max VO
₂
) can last only as long as the glycogen lasts. But there’s a catch here, and if you are an experienced endurance athlete, you know it: You can drink athletic beverages containing glucose to slow the muscle’s glycogen loss during exercise but, unfortunately, you cannot drink them fast enough. The maximum rate that ingested glucose can be metabolized during exercise is about 1 gram per minute—still not fast enough to replace what’s being lost during hard exercise. As muscle glycogen stores become depleted, you’re forced to slow down because the remaining fat stores require more oxygen to be burned. This reduced oxygen efficiency of fat compared with glucose is precisely why you must reduce your intensity once muscle glycogen reserves are severely depleted.

There is still a way out of this bottleneck. You can slow muscle glycogen loss by increasing how efficiently you burn fats and by increasing your IMT stores. Fats play a key role in how well you will perform in ultra-endurance events and bicycle road races. In long, moderate-intensity races such as these, not only do you deplete your carbohydrate reserves; you simply cannot metabolize ingested carbs (from drinks or energy bars) as fast as you are losing them. Accordingly, if you can maximize both your muscle IMT and glycogen before the race, you will be in a lot better shape during the race. Michael Vogt, PhD, and colleagues from the University of Bern in Switzerland showed that athletes consuming a 53 percent fat diet for 5 weeks were able to double their IMT stores without compromising muscle glycogen stockpiles. Further, the athletes’ endurance performance at moderate to high intensities was maintained with a significantly larger contribution of fat to energy output. These results have been consistently confirmed in the ensuing 7 years since the publication of the first edition of
The Paleo Diet for Athletes.
Interested readers may consult these scientific references listed in the References.

Your individual dietary strategy will depend upon the length and intensity of your race. If ultra-endurance events are your thing, then you may want to give a higher-fat diet a try—but make sure it contains healthy fats, not trans fats that are found in most processed and fast foods. Shorter, high-intensity races require more carbs and less fat, but it is still important that you try to maximize both IMT and muscle glycogen stores.

Now let’s tie up the loose ends. Our ancestral dietary patterns couldn’t have allowed us to restore muscle glycogen day in and day out. High glycemic load carbs on a year-round basis simply did not exist. Additionally, Stone Age people typically did not eat three meals a day. Contemporary studies of the Aché hunter-gatherers in Paraguay show that men usually ate only a single large meal in the evening. About 10 days a month they took breakfast, but they almost never had a midday meal. Women and children, on the other hand, stayed closer to camp and ate frequently throughout the day. In modern scientific experiments, the conditions the Ache men experienced (long fasting periods) have been shown to increase IMT, as have high-fat diets. Consequently, our Paleolithic relatives were much more reliant upon IMT when it came to running down animals or doing long, drawn-out, heavy work. You, on the
other hand, have the luxury of adding performance-enhancing high glycemic load carbs to your diet whenever you want. But remember the take-home message that we emphasize throughout this book: moderation and quality. Avoid refined grains and sugars and replace them with better choices at the right time, as outlined in
Chapters 4
and
9
.

Macronutrient Balance: Protein

One of the striking differences between ancestral and modern diets is the protein content. Protein makes up about 15 percent of the calories in the US diet, whereas in hunter-gatherers’ diets it was between 19 and 35 percent of total energy. Compared with fat and carbohydrate, protein is a relatively negligible fuel source during rest. Even with moderate to strenuous exercise lasting up to 2 hours, protein accounts for less than 5 percent of the energy cost of the activity. However, during the end stages of prolonged endurance events, protein can contribute up to 15 percent of the total energy cost.

The building blocks of all proteins are smaller compounds called amino acids. Before proteins can be used to produce energy in muscles, they must first be broken down into their constituent amino acids. One of these amino acids, alanine, is then released into the bloodstream, where it travels to the liver and can be converted to glucose in a process known as gluconeogenesis. However, the conversion of alanine to glucose amounts to only about 4 grams per hour—just a trickle, compared with values as high as 3 grams of glucose per minute needed during very high-intensity exercise.

Does this mean that you should forget about protein and worry only about carbs and fat when it comes to improving performance? Absolutely not. As explained in
Chapters 1
,
2
, and
9
, upping your protein intake may positively influence fatigue, muscle protein synthesis during recovery, and immune function. Also, don’t forget that meats, fish, and seafood are rich sources of zinc, iron, and vitamin B
₆
—trace nutrients that will almost certainly be low if you are following a starch and refined carb diet.

FATTY ACID BALANCE

When you adopt the Paleo Diet for Athletes, you will want to get rid of the bad fats and concentrate on the health-promoting ones. As you have seen, increasing fat in your diet may not be a bad thing when it comes to endurance performance. Getting the right kinds of fat into your diet may also improve your immune system and help lower the risk of many inflammatory diseases, heart disease, certain autoimmune diseases, and some cancers.

Chemical Structure of Fats

Like any other specialty area, you have to take some time to master the language before you can get a handle on how things work. Most athletes are concerned with their diet and know a little bit about the three major types of dietary fats: saturated, monounsaturated, and polyunsaturated. Let’s get into just a bit more detail.

Technically, all fats are called acylglycerols; each is composed of a glycerol molecule bound to 1, 2, or 3 acyl molecules. A more familiar term for an acyl molecule is “fatty acid.” So if a saturated fatty acid is attached to a glycerol molecule, it can legitimately be called a fat. If the saturated fatty acid is not connected to glycerol, then it formally is not a fat but, rather, a free fatty acid. The same holds for monounsaturated and polyunsaturated fatty acids: If they are bound to glycerol, they are fats. If not, they are free fatty acids. All free fatty acids aren’t really free; they must be linked to a protein molecule to travel in the blood.

If a single fatty acid is connected to a glycerol molecule, it is called a monoacylglycerol or monoglyceride. Two fatty acids connected to glycerol make a diacylglycerol (or diglyceride), and three fatty acids attached to glycerol are called a triacylglycerol or, more commonly, a triglyceride. Virtually all the fats you eat and almost all the fats you store in adipose (fat) tissue are triglycerides. Storage triglycerides in your fat cells can be used to fuel your muscles, but the fatty acids have to be first cleaved from the glycerol molecule and then bound to a protein molecule
(albumin) to be transported in the bloodstream as free fatty acids.

Next, let’s discuss the three major types of dietary fats, how they are labeled, how their structures vary, and how they affect your health and performance.

Saturated Fatty Acids

FIGURE 5.2