Fat Facts

Quit debating! To burn more fat, work harder or longerÔÇöor both.

By Len Kravitz, PhD
Aug 31, 2007

Weight management programs abound,
and they employ countless strategies and
approaches. But all these programs
should include three principal components:
(1) an exercise plan that incorporates
cardiovascular and resistance
training to increase caloric expenditure and
maintain muscle mass; (2) a lifestyle/
dietary approach that emphasizes balanced
nutrition and decreased caloric
intake; and (3) a behavior modification
strategy to support implementation of
the exercise and lifestyle components.
With fitness industry professionals, perhaps
the one topic—or obsession— that
will surely generate debate in the exercise
component of the plan is, What is the
best exercise fat-burning zone? This article
will attempt to bring clarity where
there is cloudiness, research where there
is perception, and guidance where there
is dissent on this contestable issue and related
matters.

Energy Balance Basics

A kilocalorie
(hereafter referred to as
a calorie) is a unit of energy, and since
energy is neither created nor destroyed
(according to the first law of thermodynamics),
the calories you eat will either
be stored somewhere in your body or expended
for fuel in metabolism for your
daily activities, occupational tasks and exercise.
This basic theory specifies that consuming
more energy than you expend will
lead to a positive energy balance—and
weight gain. Conversely, expending more
energy than you consume will lead to a
negative energy balance—and weight loss.
However, due to individual differences in
the body’s neurological, hormonal and
metabolic regulatory systems, this concept
of caloric balance does not work to precisely
the same degree in all persons.

When a person has a negative energy
balance, weight loss may come from three
body sources: water, adipose tissue (fat)
and muscle tissue. Under most circumstances,
body water will remain relatively
normal as long as regular hydration is
maintained. The goal of a weight loss plan
is to lose fat while preserving muscle mass.

Is Low-Intensity Exercise Better for Fat Burning?

We’ve all heard the claim that the best
type of cardiovascular training for burning
fat is lower-intensity exercise, which
keeps the exerciser in the so-called “fat-burning
zone.” Thompson and colleagues
(1998) have confirmed that at lower
intensities (50% VO2max), a greater percentage
of energy comes from fat than at
higher intensities (70% VO2max).
However, as long as workouts are the
same length, the total energy expenditure
will be greater, and a person will almost
always burn at least as many fat calories
(if not more), at a higher training intensity
than at a lower training intensity. In
other words, the selective use of fat as fuel
that occurs in low-intensity exercise does
not translate into greater fat loss. For
weight loss plans, fitness professionals
should focus on the exercise regime that
yields the greater total volume of calories
expended.

To further substantiate this association,
I conducted a simple experiment.
A 191-pound physically fit male student
performed 30 minutes of treadmill exercise
under two conditions: (1) at 55% of
his heart rate maximum (HRmax) and
(2) at 85% of his HRmax. The results of
this experiment were as follows:

At the higher intensity, the subject
burned more total calories, more fat calories
and more carbohydrate calories. But
not every client can exercise the way this
very fit student can. For people who are
sedentary or at orthopedic, cardiac or
health risk, high-intensity exercise may be
contraindicated. For their weight loss
exercise plans, low- to moderate-intensity
exercise should be performed for progressively
longer durations. In fact, since
most people can’t do high-intensity exercise
on a daily basis, owing to potential
overtraining and overuse concerns, perhaps
the best strategy is to integrate and
balance the low- to moderate-intensity,
long-duration workouts with high-intensity
workouts for optimal fat-calorie
burning.

Does Cardiovascular Exercise Make You a Better “Fat Burner”?

Horowitz and Klein (2000) indicate that
a number of physiological and metabolic
adaptations that occur with cardiovascular
exercise enhance fat metabolism.
These adaptations include the following:

1. An improved oxygen delivery and
extraction system (via blood flow and
capillarization) helps cells burn fat
more efficiently.

2. The sensitivity of muscle and fat cells
to epinephrine is enhanced, leading to
improved release of fatty acids (which
are the disassembled triglycerides)
into the blood and within the muscle
(where fat is in its triglyceride storage
form).

3. An augmented circulatory blood flow
system aids in the delivery of fatty
acids to the muscle.

4.
The amount of fatty acids allowed to
enter the muscle increases, making
more fat available for fuel.

5.
An improvement in the specialized
protein transporters that admit the
fatty acids into the muscle cells makes
the fat more readily available.

6.
The mitochondria, sometimes referred
to as the cells’ “fat-burning furnaces,” increase
meaningfully in number and size.

7.
The oxidative enzymes that speed up
the breakdown of fatty-acid molecules
to be used during aerobic exercise
increase.
An important take-home message for
all your students and clients is that consistent,
progressively challenging cardiovascular
exercise will truly develop their
bodies into much better fat burners.

Why is Carbohydrate the Preferred Energy Fuel?

From a caloric standpoint it seems that fat (at 9 calories per gram) should be a
much better source of fuel for exercise than carbohydrate (at 4 calories per gram).
However, carbohydrate is the most important fuel source for exercise and the only
fuel source used proficiently in both anaerobic and aerobic training. The body
prefers carbohydrate to fat during endurance exercise for two major reasons: First,
the metabolic pathways for carbohydrate breakdown (glycolysis) are much more
efficient than those for fat breakdown (mobilization, lipolysis and beta oxidation).
Second, more oxygen is required to burn fat. The energy yield of fat from 1 liter of
oxygen is 4.69 calories, as compared with a yield of 5.05 calories from carbohydrate. Thus, carbohydrate is approximately 7% more efficient as a fuel.

Where Does Resistance Training Factor In?

Research by Bryner and colleagues (1999)
has demonstrated that one of the most
important benefits of resistance exercise
in a weight loss program is the preservation
of muscle mass, even on very low
calorie diets. In addition, Andrew Hill
(2004) has shown that diet-only programs
can lower a person’s resting metabolic
rate (RMR) by 20% (which may
mean that approximately 300 fewer calories
are expended per day). Bryner’s research
demonstrates that resistance
training is one of the best protective interventions
to maintain the RMR during
a calorie-restricted weight loss program.

Fat-Burning Solution

Your clients may be gratified to know that
with consistent endurance exercise, they
truly will develop better “fat-burning furnaces”
(mitochondria) in their bodies! Try
to consistently focus workout designs on
burning the most calories possible with
the exercise plan—whether through
harder workouts; easier, longer-duration
workouts; or a combination of the two. In
addition, remember that among the many
benefits of resistance training is the fact
that it helps preserve the body’s muscle
mass and RMR in calorie-restricted states.
Consistently remind your clients, “To
burn more fat, burn more calories.”


References

Bryner, R.W., et al. 1999. Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate. Journal of the American College of Nutrition, 18 (1), 115-21.
Hill, A.J. 2004. Does dieting make you fat? British Journal of Nutrition, 92 (Suppl. 1), S15-18.
Horowitz, J., & Klein, S. 2000. Lipid metabolism during endurance exercise. American Journal of Clinical Nutrition, 72 (2, Suppl.), 558S-63S.
Thompson, D.L., et al. 1998. Substrate use during and following moderate- and low-intensity exercise: Implications for weight control. European Journal of Applied Physiology and Occupational Physiology, 78 (1), 43-49.

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Len Kravitz, PhD

Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico in Albuquerque, where he recently won the Outstanding Teacher of the Year award. Len was also honored as the 2006 Fitness Educator of the Year by the American Council on Exercise.

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