Heightened fat burning capacity -
The problem with this study is that the design of the exercise test was biased to take advantage of improved fat burning. The initial 2. But if this study had instead involved a time trial after a standard warm-up, it is unlikely that the high-fat diet would have been seen to result in better performance.
Indeed, other studies have found that a high-fat diet followed by a carbo-loading phase impairs performance in high-intensity time trials. Perhaps the best-known advocate of this approach was Phil Maffetone, an endurance sports coach who made his name by developing a training philosophy that was characterized by an extreme emphasis on the importance of fat metabolism.
Over time, Maffetone believed, the athlete would be able to swim, bike or run faster and faster at the same, low, fat-burning intensity. Research has shown that training in the fat-burning zone does improve fat-burning capacity. However, it only improves fat-burning capacity within the fat-burning zone itself—that is, at lower exercise intensities.
Indeed, despite being well adapted for fat burning, elite male marathon runners oxidize carbohydrate almost exclusively during competition.
Only slower marathon runners plus and ultramarathon runners are likely to benefit from emphasizing training in their fat-burning zone.
In summary, there is probably nothing special you need to do with your diet or your training to become a fat-burning machine and, as such, a faster racer. Proper training will automatically increase your fat-burning capacity, but this adaptation will not directly influence your performance in races lasting less than several hours.
This enables them to use fat as a fuel when their carbohydrate stores become limited. In contrast, patients with obesity, insulin resistance and type II diabetes may have an impaired capacity to oxidise fat. As a result, fatty acids may be stored in their muscles and in other tissues.
This accumulation of lipid and its metabolites in the muscle may interfere with the insulin-signalling cascade and cause insulin resistance. It is therefore important to understand the factors that regulate fat metabolism, and the ways to increase fat oxidation in patients and athletes.
Fats are stored mostly in subcutaneous adipose tissue, but we also have small stores in the muscle itself intramuscular triglycerides. At the onset of exercise, neuronal beta-adrenergic stimulation will increase lipolysis the breakdown of fats into fatty acids and glycerol in adipose tissue and muscle.
Catecholamines such as adrenaline and noradrenaline may also rise and contribute to the stimulation of lipolysis. As soon as exercise begins, fatty acids are mobilised. Adipose tissue fatty acids have to be transported from the fat cell to the muscle, be transported across the muscle membrane and then be transported across the mitochondrial membrane for oxidation.
The triglycerides stored in muscle undergo similar lipolysis and these fatty acids can be transported into the mitochondria as well.
During exercise, a mixture of fatty acids derived from adipocytes and intramuscular stores is used. There is evidence that shows that trained individuals store more intramuscular fat and use this more as a source of energy during exercise 1. Fat oxidation is regulated at various steps of this process.
Lipolysis is affected by many factors but is mostly regulated by hormones stimulated by catecholamines and inhibited by insulin. The transport of fatty acids is also dependent on blood supply to the adipose and muscle tissues, as well as the uptake of fatty acids into the muscle and into the mitochondria.
By inhibiting mobilisation of fatty acids or the transport of these fatty acids, we can reduce fat metabolism. However, are there also ways in which we can stimulate these steps and promote fat metabolism? Exercise intensity — One of the most important factors that determines the rate of fat oxidation during exercise is the intensity.
Although several studies have described the relationship between exercise intensity and fat oxidation, only recently was this relationship studied over a wide range of intensities 2.
In absolute terms, carbohydrate oxidation increases proportionally with exercise intensity, whereas the rate of fat oxidation initially increases, but decreases again at higher exercise intensities see figure 1.
So, although it is often claimed that you have to exercise at low intensities to oxidise fat, this is not necessarily true. However, the inter-individual variation is very large.
However, very little research has been done. Recently we used this intensity in a training study with obese individuals. Compared with interval training, their fat oxidation and insulin sensitivity improved more after four weeks steady-state exercise three times per week at an intensity that equalled their individual Fatmax 4.
Dietary effects — The other important factor is diet. A diet high in carbohydrate will suppress fat oxidation, and a diet low in carbohydrate will result in high fat oxidation rates. This effect of insulin on fat oxidation may last as long as six to eight hours after a meal, and this means that the highest fat oxidation rates can be achieved after an overnight fast.
Endurance athletes have often used exercise without breakfast as a way to increase the fat-oxidative capacity of the muscle. Recently, a study was performed at the University of Leuven in Belgium, in which scientists investigated the effect of a six-week endurance training programme carried out for three days per week, each session lasting one to two hours 6.
The participants trained in either the fasted or carbohydrate-fed state. When training was conducted in the fasted state, the researchers observed a decrease in muscle glycogen use, while the activity of various proteins involved in fat metabolism was increased.
However, fat oxidation during exercise was the same in the two groups. It is possible, though, that there are small but significant changes in fat metabolism after fasted training; but, in this study, changes in fat oxidation might have been masked by the fact that these subjects received carbohydrate during their experimental trials.
It must also be noted that training after an overnight fast may reduce your exercise capacity and may therefore only be suitable for low- to moderate- intensity exercise sessions.
The efficacy of such training for weight reduction is also not known. Duration of exercise — It has long been established that oxidation becomes increasingly important as exercise progresses. During ultra-endurance exercise, fat oxidation can reach peaks of 1 gram per minute, although as noted in Dietary effects fat oxidation may be reduced if carbohydrate is ingested before or during exercise.
In terms of weight loss, the duration of exercise may be one of the key factors as it is also the most effective way to increase energy expenditure. Mode of exercise — The exercise modality also has an effect on fat oxidation.
Fat oxidation has been shown to be higher for a given oxygen uptake during walking and running, compared with cycling 7. The reason for this is not known, but it has been suggested that it is related to the greater power output per muscle fibre in cycling compared to that in running.
Gender differences — Although some studies in the literature have found no gender differences in metabolism, the majority of studies now indicate higher rates of fat oxidation in women. In a study that compared men and women over a wide range of exercise intensities, it was shown that the women had higher rates of fat oxidation over the entire range of intensities, and that their fat oxidation peaked at a slightly higher intensity 8.
The differences, however, are small and may not be of any physiological significance. There are many nutrition supplements on the market that claim to increase fat oxidation. These supplements include caffeine, carnitine, hydroxycitric acid HCA , chromium, conjugated linoleic acid CLA , guarana, citrus aurantium, Asian ginseng, cayenne pepper, coleus forskholii, glucomannan, green tea, psyllium and pyruvate.
With few exceptions, there is little evidence that these supplements, which are marketed as fat burners, actually increase fat oxidation during exercise see table 1. One of the few exceptions however may be green tea extracts.
The mechanisms of this are not well understood but it is likely that the active ingredient in green tea, called epigallocatechin gallate EGCG — a powerful polyphenol with antioxidant properties inhibits the enzyme catechol O-methyltransferase COMT , which is responsible for the breakdown of noradrenaline.
This in turn may result in higher concentrations of noradrenaline and stimulation of lipolysis, making more fatty acids available for oxidation. Environment — Environmental conditions can also influence the type of fuel used.
It is known that exercise in a hot environment will increase glycogen use and reduce fat oxidation, and something similar can be observed at high altitude. Similarly, when it is extremely cold, and especially when shivering, carbohydrate metabolism appears to be stimulated at the expense of fat metabolism.
At present, the only proven way to increase fat oxidation during exercise is to perform regular physical activity. Exercise training will up-regulate the enzymes of the fat oxidation pathways, increase mitochondrial mass, increase blood flow, etc.
Research has shown that as little as four weeks of regular exercise three times per week for minutes can increase fat oxidation rates and cause favourable enzymatic changes However, too little information is available to draw any conclusions about the optimal training programme to achieve these effects.
In one study we investigated maximal rates of fat oxidation in subjects with varying fitness levels. In this study, we had obese and sedentary individuals, as well as professional cyclists 9. Humans also produce this protein. One study found that people who were more sedentary produced less irisin than those who exercised more often.
Specifically, levels are increased when people do more intense aerobic interval training. Exercise is highly recommended by doctors for heart health and weight management. Current physical activity guidelines for adults include doing one of the following every week:.
But exercise still has many health benefits. More research is needed on humans. Researchers are still trying to understand the genes that control how white and brown fat develops. In one study , scientists engineered mice to be born with very little brown fat by limiting a protein called Type 1A BMP-receptor.
When exposed to cold, the mice created brown fat from their white fat and muscles anyway, showing the power of recruitment. Researchers have also discovered that a certain protein called early B-cell factor-2 Ebf2 might play a key role in building brown fat.
When engineered mice had exposure to high levels of Ebf2, it transformed white fat to brown fat. These cells consumed more oxygen, which shows that the brown fat was indeed producing heat and burning calories. A review on various studies has shown that brown fat burns calories and may help control blood sugar and improve insulin levels, decreasing the risk for type 2 diabetes.
It may also help with removing fats from the blood, decreasing the risk for hyperlipidemia. More research is needed before doctors can hand out a pill or other quick fix to convert white fat to brown. Before you start taking ice baths, eating more, or turning down your thermostat, start by making small changes to your diet and trying some low impact exercises.
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