You are now anaerobic. Fuel reliance switches predominantly to carbohydrates, and the result is the accumulation of lactic acid. Lactic acid inhibits the enzymes that break down fat and therefore reduces fat metabolism. If you go out for a minute run at 10K race pace, you will be burning less fat and generating more waste products than if you ran those 45 minutes at only a 60 percent effort.

Daily hard efforts will result in accumulation of waste products and decreased recovery, and lead to declining performances.

His fat metabolism is augmented, there is a substantially reduced reliance on glycogen, and his glycogen stores are larger. He again decides to test his ability to run at 65 percent of his maximum. Before the test he makes sure to get plenty of carbohydrates in his diet so that his leg muscles and liver are loaded with glycogen.

This time he was able to continue for three hours. His skeletal, connective, and muscle tissues; his metabolism; and his cardiovascular, nervous, and endocrine systems are now prepared for some faster training.

His next step is to focus on increasing his endurance running speed and reducing his lactate production. Endurance races are aerobic races. Marathons tend to be run at just below the level where you start to accumulate lactic acid, which is known as the anaerobic threshold AT.

How many times have you started a race too fast and gone anaerobic, only to suffer later and run slower than you planned or even had to drop out?

With a higher AT, you will be able to sustain faster marathon and ultramarathon paces. Elite world-class marathoners often have such a highly developed fat-burning engine that they can run marathons at 85 percent or higher of their maximum.

For the rest of us, 75 to 80 percent is a realistic goal. Anaerobic threshold training augments the basic fat metabolism you have spent so much time developing. The result is faster running speeds over the long haul. A measured dose of faster, anaerobic training will teach your muscles and blood to metabolize and buffer lactic acid.

The goal is to generate a manageable quantity of lactic acid that your muscles can dispose of easily and permit a sufficiently long training session and quick recovery. Venturing too far into the anaerobic zone will generate too much lactic acid, reduce the amount of work you can do within your training session, and risk lasting fatigue and overreaching.

Faster, sustained running at 80 to 85 percent and mile repeats are good methods to increase lactate tolerance. Oglesby recommends tempo runs of 10 to 12 miles at 15 to 30 seconds per mile faster than goal marathon race pace.

An added benefit of these tempo runs is that the marathon pace feels easier and more manageable. A recent study examined the effect of high-intensity interval sessions on fat and carbohydrate metabolism and lactate concentrations in cyclists who had been training two to three hours per day for years.

They replaced some of their endurance miles with two weekly sessions of x 5-minute intervals with 1 minute of recovery between.

After six weeks, the percentage of energy coming from fat during a one-hour trial had increased from 6 percent to 13 percent. How well this applies to a race lasting more than two hours is unclear. I would like to emphasize that high-intensity training builds on the increased strength, resilience, and fat metabolism developed during those long, high-quality aerobic miles.

Jumping into AT training before your body is sufficiently prepared will not produce the desired results: fast marathons. It is best to start an exercise session with stable, fasting blood glucose levels and higher blood fat levels. Glucose is a powerful regulator of fat metabolism.

The higher the glucose content of the blood, the lower the fat metabolism. High blood glucose levels are generated from dietary carbohydrates. This effect is associated with insulin.

High blood glucose stimulates the hormone insulin to be released from the pancreas. Insulin is a storage and growth hormone. Its main job is to reduce blood glucose but it also acts to store fat and protein.

In the process, insulin directly blocks removal of fat from fat deposits. These deposits are an important source of fat for exercising muscle. Insulin also reduces fat burning within the muscle.

Therefore, increased insulin is considered to be antagonistic to fat combustion during exercise. In an interesting piece of research, investigators at the University of Limburg in the Netherlands and at the University of Texas collaborated to determine whether high blood glucose and high insulin levels reduce the amount of fat burned during moderate-level exercise.

A group of endurance-trained men cycled for 40 minutes at an aerobic 50 percent of maximum after an overnight fast. On another day, they ingested a drink containing grams of glucose at 60 minutes before and then again at 10 minutes prior to the exercise test.

This is a carbohydrate equivalent of drinking one and one-half liters of Gatorade an hour before a race and again 10 minutes before the start.

While this may not mimic real-life situations, what the researchers found was telling. Fat metabolism was substantially reduced for the full 40 minutes of the exercise after the carbohydrate load. While most people would not eat that much carbohydrate before a run, it is common for people to eat a sports bar, bagel, or banana in the hour prior to training.

Try to avoid eating for at least two hours before a run. It takes as little as 20 grams of ingested carbohydrate to raise insulin and reduce fat as fuel. If you have nutrition awareness or read the nutrition labels on foods, you will know that a couple of slices of bread, a banana, a sports bar, or a soda each delivers more than 20 grams of carbohydrate.

Fasting increases blood fat levels. Running after your overnight fast will increase fat burning. A cup of coffee beforehand may boost it even higher. Once exercise has started, eating carbohydrates does not generate a substantive insulin response. If you are starting a long run lasting two hours or more on an empty stomach, you may want to eat a sports gel or bar after 20 to 30 minutes throughout the run.

Otherwise you will be faced with the nausea and fatigue of low blood sugar and have a poor training session. If you tend toward hypoglycemia when you get up in the morning, you may want to eat something in the minutes immediately before you head out the door.

It takes 30 minutes for insulin levels to peak. However, before a long race or run you will have more endurance and perform better if you eat a meal containing carbohydrate two to three hours before. Early in the morning, your liver glycogen stores, which supply blood glucose, have been depleted by the overnight fast.

The brain and nervous system rely on blood glucose for energy. If you start a marathon without replenishing these stores, you will bonk. The two-hour time interval is sufficient to reduce blood glucose levels back to normal and restore fat metabolism. There has been considerable research in the past decade on the effect of diet composition on endurance.

Prior to now, endurance athletes usually followed a high-carbohydrate diet with the rationale that enhanced glycogen stores are known to fuel superior training and marathon race performances.

Most sports nutritionists recommend a diet that supplies 6 to 8 grams of carbohydrates per kilogram of body weight. These levels of dietary carbohydrate can easily reach to grams per day. This adds up to 1, to 2, calories of carbohydrate per day.

The downside of a high-carbohydrate diet, especially a diet loaded with sugar, is reduced fat metabolism and fatigue. This is largely due to chronically stimulated insulin levels. The effects of insulin can last up to eight hours, especially after a big dose of carbohydrates, such as you might get from a big plate of spaghetti and rolls followed by a bowl of sorbet.

Initially, studies found that high-fat diets, where fats supply 60 percent or more of the calories, showed promise as a means to better endurance.

Fat burning is increased on high-fat diets, even at rest. Exercise tests showed higher endurance in subjects who had been eating high-fat diets in comparison with high-carbohydrate diets.

At issue, however, was the intensity of exercise used for the tests. High-fat diets improved endurance at relatively low-intensity levels.

When the intensity was increased to mirror race situations, the advantage disappeared. The higher- intensity exercise required more carbohydrate, and the subjects simply lacked adequate glycogen to continue for extended periods.

We now know that both high-carbohydrate and high-fat diets cause fatigue and poor performances. The best diet is probably somewhere in between: one that supplies enough fat to stimulate fat metabolism and maintain production of testosterone and estrogen and also supplies enough carbohydrate to keep the brain and nervous system happy and the glycogen stores filled.

Many sports scientists are recommending a basic diet that supplies 50 percent carbohydrate, 30 percent fat, and 20 percent protein, with additional carbohydrates after hard or long-duration training. There are still many unanswered questions regarding nutrition and endurance sports performance. Before a marathon or longer race, will fat loading in combination with glycogen loading boost performance?

After hard or long training, should you also concentrate on replenishment of fat stores in the muscles? What type of fat, saturated or unsaturated, is burned for fuel? Will eating fat during races that last four hours or more benefit performance outcomes?

What profile of fats in the basic diet is best for an athlete? The skeletal muscle membrane is made of fat. The composition of this membrane directly reflects the profile of fats in the diet.

A diet high in saturated fats will generate a more solid, less fluid membrane. A membrane that incorporates more unsaturated fats is more fluid, allowing a more efficient flux of oxygen, water, fat, and glucose.

New theories hold that these membranes are more leaky and require more energy to maintain. Conceivably then, a diet too high in either saturated or unsaturated fats could be detrimental to endurance performance.

While there are new training methods being developed to enhance marathon performance, you will find substantial success with theories that are now 40 years old.

Our cells can burn amino acids as fuel and convert them into sugar and fat. Because food has not always been readily available, humans and other animals have evolved ways to store fuel reserves in their bodies.

When food is plentiful, the body packs away extra calories in fat reserves. The stored fat fuels the body when food is scarce. But why does the body go through the trouble of converting amino acids and sugars to fat for storage?

Wouldn't it make more sense to store more proteins and glycogen? It turns out that fat is a much more efficient way to store energy. Fat has about 9 calories per gram, and protein and carbohydrate have just 4.

In living tissue, this difference is even greater. Fat stored in tissue contains very little water. In contrast, every gram of glycogen the storage form for carbohydrate holds 2 grams of water.

Stored in tissue, one pound grams of fat holds about 4, calories, which is about 2 days' worth of energy. A pound of hydrated glycogen holds just calories. A typical healthy man carries about 24 pounds 11 kg of fat. Stored as glycogen, the same number of calories would weigh pounds 66 kg!

Paradoxically, fat keeps us leaner. Berg, J. Biochemistry, fifth edition. New York: W. Food and Nutrition Board, Institute of Medicine, National Academies year. Dietary Reference Intakes DRIs : Estimated Average Requirements.

Fulgoni III, V. Current protein intake in America: analysis of the National Health and Nutrition Examinatin Survey, The American Journal of Clinical Nutrition, , Marieb, E. Human Anatomy and Physiology, eighth edition. San Francisco: Benjamin Cummings. Home Metabolism: From Food To Fuel Building, Burning, and Storing: How Cells Use Food.

Building, Burning, and Storing: How Cells Use Food. Related content No single cell type carries out all of the processes shown above. To learn more, visit Metabolic pathways Amino acids are used for building proteins through a process called translation. The Fat Treadmill. Related content Fat tissue does more than just store energy.

Like groceries on a shelf, fats are constantly moving in and out of storage. Too Much Protein Can Make You Fat. Related content Sugars consumed in excess are also readily converted to fat for storage.

Therefore, people who are taking medications or have a condition like heart disease or diabetes should seek advice from their healthcare provider before beginning a fat fast and avoid doing this diet without medical supervision. The technique is also not recommended for women who are pregnant or breastfeeding or for people considered cholesterol hyper-responders, as the diet may lead to a significant increase in cholesterol levels in susceptible individuals 16 , As there is no research on the safety and efficacy of fat fasting, the potential risks associated with this eating pattern are unknown.

The risks of fat fasting are not well known. If you have a medical condition or take medications, you should avoid fat fasting. Ketogenic diets have many powerful health benefits, but some people have trouble getting into ketosis.

Here are 7 tips for how to get into ketosis. Some fats are better for you than others and may even promote good heart health. Know the difference to determine which fats to avoid, and which to…. The ketogenic diet is a very low carb diet with numerous health benefits.

Discover 20 nutritious foods you can eat on keto. The ketogenic diet keto is a low-carb, high-fat diet that causes weight loss and provides numerous health benefits. This is a detailed beginner's…. Losing or maintaining weight can be challenging, especially with so many tasty food options available.

Here are 11 foods that can contribute to weight…. Ketosis is a metabolic state that can be caused by a low-carb or ketogenic diet.

Here are 10 signs and symptoms that you're in ketosis. One of the best things about the low-carb way of eating is all the delicious foods you can eat.

Here are 6 "indulgent" foods that are low-carb. Ketosis is a natural metabolic state that your body enters when following a very low carb diet or during starvation.

This article explores ketosis and…. When your body reaches ketosis on a ketogenic diet, it uses ketones as an alternative energy source.

This article tells you how long it takes to enter…. Discover which diet is best for managing your diabetes. A Quiz for Teens Are You a Workaholic? How Well Do You Sleep?

Health Conditions Discover Plan Connect. Nutrition Evidence Based What Is Fat Fasting, and Is It Good for You? By Helen West, RD — Updated on April 29, What it is Fat burning Healthy? Share on Pinterest. What is fat fasting? How does it help you burn fat? Is fat fasting healthy?

What can you eat on a fat fast? Who should do a fat fast? Side effects and risks. The bottom line. Share this article. Read this next. Good Fats, Bad Fats, and Heart Disease. Medically reviewed by Adrienne Seitz, MS, RD, LDN.

By SaVanna Shoemaker, MS, RDN, LD and Franziska Spritzler. Additionally, it may be difficult to continue performance at high intensities. As of now, there is no consensus on the effects of a LCHF diet in endurance athletes. Therefore, there are no set guidelines for following a low carb high fat diet: it is up to you to experiment what works for you.

Keep in mind that this article is for educational purposes only; we are not preaching a HFLC diet! Whatever you do, still keep in mind other aspects of good nutrition , including a diversity of food sources, less processed foods, complete protein sources, and high fiber foods! Fast worldwide delivery.

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Previous Next. Your body using fat If you are an endurance athlete of any kind, the idea of a high fat diet might sound appealing since our bodies store vastly more fat than glucose, allowing for a more sustained source of energy.

Factors affecting fat oxidation There are several factors that affect fat oxidation efficiency, the most important one being exercise intensity and duration. The verdict on LCHF diets Currently, there is very little research out there that is in favor of a high fat diet for endurance sport performance.

Disadvantages of fueling with fat In non-fat adapted athletes, low carbohydrate availability increases muscle protein breakdown and in severe cases, can eventually lead to a loss of skeletal muscle mass.

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