What Causes the Body to Burn Fat?

Image credit: 123rf.com

Image credit: 123rf.com

At this year’s IDEA World Fitness Convention in Anaheim, CA, many new and exciting ideas flooded my brain. And even though Disneyland was right next door, for me nothing could compare to the pageantry at the Anaheim Convention Center, where 12,000 attendees from 63 countries mingled and made their way to a myriad of offerings. Some events were hands-on, while others were more lecture style–all were inspiring in their own way. It felt good to be among so many “tribe” members, all of us looking to connect and expand our sphere of knowledge.

Dr. Len Kravits

Dr. Len Kravitz

With so much to report, it’s difficult to pick a topic to feature here, but I decided to boil down some new findings presented by Dr. Len Kravitz, an exercise science professor at the University of New Mexico. Kravitz comes across like a slightly toned-down Richard Simmons, trading sparkly tank tops and shorts for flamboyant polyester shirts, plaid pants, and bolo ties!

But what he may lack in fashion sense he more than makes up in his knowledge of nutrition and exercise. Indeed, Kravitz, 58, is an international fitness expert who has written hundreds of peer-reviewed articles and delivered lectures on every topic imaginable. His book, “Anybody’s Guide to Total Fitness,” is now in its ninth edition.

Vibrating with excitement about his latest study, “The Physiology of Fat Loss,” published in IDEA Fitness Journal earlier this year, he addressed the packed conference room of trainers eager to be infected with his enthusiasm.

The Inside Story on Fat and Fat Burn
“The average person has 40 billion fat cells,” Dr. Kravitz began, adding that fat “is best known for its role as an energy reserve.” Well, that may be true for PhDs, but for my clients, fat is best known as the despised nemesis that intractably wraps itself ‘round their midsections or otherwise clings to hips, butts, and thighs. And while fat may have biological roles of value, the main concern among my clients is how to make it go away.

Kravitz was getting to that. Depending on energy supply and demand, fat can either be stored in fat storage cells called adipocytes or released from these cells back into the blood as fatty acids and carried to muscle cells by carrier proteins, primarily albumin. When they reach the small capillaries surrounding working muscle, these fatty acids can be transported into the muscle cells for use as energy. More specifically, for our bodies to “burn” fat, the fatty acids must be transported into a muscle cell’s mitochondria–“the fat-burning furnaces in the body’s cells” and the only place where fat-storage molecules get completely broken down. a process known as lipolysis.

“Exercise is the best way to mobilize fat for energy!” Dr. Kravitz exclaimed, adding that “nothing on the market can compare.”

Regular exercise not only increases mitochondrial density in muscle cells but also increases the transport proteins, oxidative enzymes, and density of small capillaries that feed the fatty acid “fuel” to our fat-burning furnaces. These combined effects from regular exercise mean that a conditioned exerciser will burn more fatty acids as a percentage of her total workout burn than an unconditioned couch potato will, doing the exact same workout!

“A meal with low glycemic-index carbs has been shown to elicit a greater rate of fat oxidation during exercise and after, because high glycemic foods promote insulin production, and insulin impairs fat metabolism.” (Contact me for a list–Jen)


Exercise Intensity Matters

So when do you burn the most fat? According to Dr. Kravitz, during the workout “we burn the most fat when exercising at low to moderate intensity.” When we first start exercising (i.e., warming up at very low intensity–hopefully you’re all doing this!), most of the fatty acids being used are coming from what’s already in the blood. But as intensity increases to the moderate level (e.g., brisk walking where you can still talk but maybe not sing), the body shifts to using fatty acids coming from those adipocytes—the fat we want to lose. “Consistent cardio increases this shift better than any pill out there,” Dr. Kravitz noted. “To burn the most calories and the most amount of fat, keep your workout comfortable but challenging.”

His advice does not ignore the value of folding in short-duration high-intensity intervals as well. During high-to-peak intensity exercise, the muscle mitochondria shift to burning a higher fraction of carbohydrate vs. fat, just to meet the surge in energy demand. But afterward, the body uses lipolysis (fat burn) to help replace that carbohydrate “surge fuel,” which increases total caloric expenditure and fat loss, as discussed here.

Therefore, a combination of high-intensity intervals plus low- to moderate-intensity continuous aerobic exercise in one workout is optimal for overall fat burn. Moreover, different modes of exercise build up different pieces of that complex metabolic chain that gets fat out of storage and to the furnaces. Resistance training, for example, produces good post-exercise calorie burn, among its many other benefits. (You didn’t think a blog of mine would fail to mention resistance training, did you?)

So, what’s stopping you from stoking up your fat-burning furnaces? Get moving! Here are some exercise combos proven to work well for calorie and fat burn. I encourage everyone to adopt this “mixed” approach for most of their cardio workouts:

Split training (45 min)
1.  5 min warmup
2.  15 min of high-intensity cardio (e.g., treadmill/elliptical/bike/etc.)
3.  5 min of of recovery (same cardio type slowed down)
4.  Repeat #2
5.  Repeat #3
6.  5 min cooldown/stretch

HIIT with variable recovery (29 min)
1.  5 min warmup
2.  4 min of intense cardio (e.g., on treadmill/elliptical/bike/etc.)
3.  4 min recovery (same exercise, or walking)
4.  Repeat #2
5.  2 min recovery
6.  Repeat #2
7.  1 min recovery
8.  5 min cooldown/stretch

The 3-in-1 workout (~35 min)
1.  10 min warmup of light exercise
2.  30-sec sprint of any cardio
3.  1 min of “active” rest (don’t stop completely but slow it down)
4.  15 min of slow aerobics, any mode
5.  1 min sprint of any cardio
6.  3 min of active rest
7.  5 min cooldown/stretch

Keep moving! — Jen


Leave a Reply

Your email address will not be published. Required fields are marked *