By Dr. Mercola

The vast majority of doctors, dietitians, and personal trainers believe that when you burn fat during exercise, that fat is being used up as fuel for energy or heat. Some believe it’s excreted through urine or feces, while others think the fat is turned into muscle.

All of these ideas are to some degree incorrect, according to Ruben Meerman, a physicist, and Andrew Brown, a biochemist specializing in lipids, who say there’s “surprising ignorance and confusion about the metabolic process of weight loss.”

When You Lose Weight, Where Does the Fat Go?

Their calculations, showing where the fat really goes when you lose weight, was recently published in the journal BMJ.^1,2 As explained by Medical News Today:³

“Excess dietary carbohydrates and protein are converted to a type of fat called triglyceride. When people attempt to lose weight, they are attempting to metabolize these triglycerides while keeping their fat-free mass intact…

Triglycerides are comprised of three types of atoms: carbon, hydrogen and oxygen. Triglyceride molecules can be broken down only by unlocking these atoms, through a process known as oxidation.

The researchers chose to follow the path of these atoms when leaving the body. They found that when 10 kg of fat were oxidized, 8.4 kg were converted and excreted as carbon dioxide (CO₂) via the lungs, and 1.6 kg became water (H₂0).

In order for 10 kg of human fat to be oxidized, the researchers calculated that 29 kg of oxygen must be inhaled. Oxidation then produces a total of 28 kg of CO₂ and 11 kg of H₂0.”

The researchers note that this is not new to science—rather the process has simply been misunderstood. The equation does involve release of energy; it’s just that the process isn’t as direct as one might think. According to the law of conservation of mass, it’s actually quite difficult to convert matter into energy.

As noted by The Atlantic:⁴ “If you were able to convert your fat stores [directly] into energy, you would explode in a glorious, catastrophic spectacle…” According to their calculations, you basically exhale 84 percent of your lost fat. The remaining 16 percent is metabolized into water, which is excreted through sweat and urine.

The authors estimate that by substituting one hour of sedentary lounging with one hour of moderate exercise—to increase your respiratory rate—your metabolic rate is increased sevenfold. However, they note that you can easily hamper any potential weight loss by eating too much food—and I would stress, by eating the wrong kinds of foods.

Your Food Choices Make a Huge Difference

It’s important to recognize that most people who struggle with excess weight have some degree of insulin and leptin resistance. Leptin is a hormone that helps you regulate your appetite. When your leptin levels rise, it signals your body that you’re full, so you’ll stop eating.

As you become resistant to the effects of leptin, you end up overeating, as your body gradually loses its ability to “hear” the signals leptin sends out. Dr. Richard Johnson’s research clearly shows that refined sugar (in particular processed fructose) is exceptionally effective at causing leptin resistance. Fructose also effectively blocks the burning of fat.

Basically, if you are insulin or leptin resistant, as long as you keep eating fructose and grains, you’re programming your body to create and store fat. This is one of the key reasons why, if you are overweight, you’d be wise to restrict your fructose consumption to about 15 to 25 grams of fructose per day from all sources.

This means switching out most processed foods for whole, unprocessed foods, and avoiding any and all sweetened beverages. Clean pure water is really the only type of fluid your body needs. For further dietary guidance, please see my comprehensive nutrition plan.

If you’re insulin/leptin resistant and/or are overweight, you can also greatly boost your body’s fat-burning potential by incorporating intermittent fasting, as it helps reset your body to use fat instead of sugar as its primary fuel. It is by far the most effective way I know of to shed unwanted fat and eliminate your sugar cravings.

Exercising in a fasted state (such as first thing in the morning) will bring it up yet another notch. A simple way to get started with intermittent fasting is to simply omit breakfast, making lunch the first meal of your day.

Maintain this daily eating schedule until your insulin/leptin resistance improves (weight, blood pressure, cholesterol ratios, or diabetes normalizes). After that, just do it as often as you need to maintain your healthy state.

White versus Brown Fat

While we’re on the topic of fat, it’s worth noting that there are different kinds of fat cells in your body, and from a metabolic standpoint, they respond differently. They even appear to have different biological functions. None of this was discussed in the featured research, but it likely also plays a role in the big scheme of things. For a number of years, scientists have been studying so-called “brown fat“—a type of fat that generates heat that burns energy instead of storing it. So-called “white fat” is the kind that is primarily stored, and because it’s also difficult to burn off, it tends to cause obesity. Research has shown that certain groups of people tend to have more brown fat than others, and there appears to be direct correlations between the activation of brown fat and metabolic measures of good health. For example:

• Slender people have more brown fat than obese people do
• Younger people have more brown fat than elderly people
• People with normal blood sugar levels have more brown fat than those with high blood sugar

How to Transform White Fat into Healthier Brown Fat

Newborns have a supply of brown fat to keep warm, but most of these stores are lost by the time adulthood is reached. However, although you have far less of it as an adult, scientists have found that you can activate the brown fat still present in your body by exposing yourself to cold temperatures. This has the effect of causing your body to burn more calories to keep warm, and there’s evidence suggesting ice therapy can be helpful for boosting weight loss. Animal research has also shown that animals convert white fat into brown fat simply by exercising.

The study,⁵ published in the journal Disease Models and Mechanism, found that during exercise the animals’ muscles released an enzyme called irisin, which triggered the conversion of white fat cells to brown. Preliminary studies presented at the 2013 annual meeting of the American Diabetes Association revealed that this holds true in humans as well. Among men, the benefits were found after 12 weeks of training on an exercise bike. One of the researchers, a postdoctoral fellow at Joslin Diabetes Center, said:⁶

“Our results showed that exercise doesn’t just have beneficial effects on muscle, it also affects fat… It’s clear that when fat gets trained, it becomes browner and more metabolically active. We think there are factors being released into the bloodstream from the healthier fat that are working on other tissues.”

As you can see, the human metabolism is extremely complex. On the one hand, exercise helps convert unhealthy white fat into healthier, heat-producing and more metabolically active brown fat. Exercise also increases the oxidation of fat, which then leaves your body via your lungs, in the form of carbon dioxide, and your bodily fluids, in the form of water. What’s not so complex however, is how to optimize your metabolism—even if you don’t understand the exact mechanisms involved. Following simple basics described below will catalyze your body’s ability to achieve your ideal weight and leanness.

Your Weight Reflects Your Lifestyle Choices

Simply eating fewer calories and exercising more usually doesn’t work very well, and the reason for that is because not all calories are the same. As mentioned, processed fructose in particular causes leptin resistance far more effectively than other sugars, with refined sugar coming in close second. Glucose is not nearly as harmful in comparison. Fructose also blocks the burning of fat. So, instead of focusing on calories, you need to address the quality of the foods you eat, and avoid chemical exposures. Endocrine-disrupting chemicals such as BPA and phthalates, for example, can cause or exacerbate weight gain. Following is a short list of proactive, easy-to-remember guidelines that can go a long way toward improving your health, nutrition, and body weight.

• Exercise regularly, and stay active all day long: Engage in high-intensity Peak Fitness exercise to burn fat and increase muscle mass (a natural fat burner). Also, strive to sit less (much less—ideally no more than three hours a day) and walk 7,000 to 10,000 steps a day in addition to your regular exercise program.
• Consider intermittent fasting: If you’re insulin/leptin resistant and/or are overweight, boost your body’s fat-burning potential by incorporating intermittent fasting. This is one of the most powerful approaches to reverse insulin resistance. It is only necessary to do until your insulin resistance resolves.
• Buy real food, preferably whole organic and locally grown, and cook from scratch. Ditching processed foods will automatically reduce your sugar consumption, which is the root cause of insulin resistance and weight gain. If you buy organic produce, you’ll also cut your exposure to pesticides and genetically engineered ingredients, and in ditching processed foods, you’ll automatically avoid artificial sweeteners and harmful processed fats like trans fats and vegetable oils (such as peanut, corn, and soy oil), the latter of which actually degrades into oxidation products when heated that may be more harmful than trans fat.

That said, most people do need upwards of 50-85 percent healthy fats in their diet for optimal health. Sources of healthy fats to add to your diet include avocados, butter made from raw grass-fed organic milk, raw organic dairy, coconuts and coconut oil, unheated organic nut oils, raw nuts and seeds, organic pastured egg yolks, and grass-fed meats. For more detailed dietary advice, please see my free Optimized Nutrition Plan.

• Opt for organic grass-fed meats to avoid genetically engineered ingredients, pesticides, hormones, antibiotics, and other growth promoting drugs.
• Opt for glass packaging and storage containers to avoid endocrine disrupting chemicals.