Low-Carbohydrate Diets Promote a More Favorable Body Composition Than Low-Fat Diets
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Low-Carbohydrate Diets
Promote a More
Favorable Body
Composition Than
Low-Fat Diets
Jeff S. Volek, PhD, RD, Erin E. Quann, PhD, RD, and Cassandra E. Forsythe, PhD, RD
Department of Kinesiology, University of Connecticut, Storrs, Connecticut
SUMMARY important for enhancing power pro- no effect independent of total energy).
duction and mechanical efficiency. In respect to body composition, con-
A PRIMARY CONCERN WITH
Lean body mass, specifically muscle vincing evidence of the importance of
CONVENTIONAL WEIGHT LOSS
mass, contributes directly to force pro- macronutrient composition was pre-
APPROACHES IS THE LOSS OF duction capacity and physical perfor- sented in a comprehensive meta-
LEAN BODY MASS THAT OCCURS mance as well as insulin sensitivity and regression of 87 diet trials (10). The
WHEN FAT MASS IS DECREASED. general metabolic health. There are authors concluded that diets lower in
CONSUMING MODERATE also aesthetic and psychological bene- carbohydrate were associated with
PROTEIN, WHILE RESTRICTING fits associated with improvements in greater fat loss and diets higher in
CARBOHYDRATE, ALLOWS FOR body composition. protein resulted in better preservation
GREATER PRESERVATION OF of lean body mass during weight loss.
Most weight loss approaches that
LEAN BODY MASS. A Furthermore, these effects were in-
decrease fat mass also result in an
LOW-CARBOHYDRATE DIET IN
undesirable loss of lean body mass. In dependent of energy intake and par-
CONJUNCTION WITH PERIODIZED fact, about one-quarter of the weight ticipation in exercise.
RESISTANCE TRAINING loss achieved through typical low-fat We have consistently shown in our
PROMOTES GREATER FAT LOSS diet approaches is from lean body mass work that very low carbohydrate
WHILE PRESERVING LEAN BODY (11,9). Weight loss interventions that ketogenic diets result in greater weight
MASS AND PROMOTING ROBUST preserve lean body mass while re- loss and fat loss compared with low-fat
IMPROVEMENTS IN METABOLIC ducing fat mass are preferred. The diets. In overweight men and women,
HEALTH. combination of caloric restriction and we have repeatedly observed a 2-fold
exercise can have a strong effect on greater weight loss and fat loss in
improving body composition, but the subjects restricting dietary carbohy-
INTRODUCTION type of diet and training program has drate versus fat despite similar caloric
he proportions of fat and lean a major influence on the magnitude of restriction between the diets (22,21).
T body mass determine an indi-
vidual’s body composition. The
goal of many athletes and nonathletes
change. This brief review will focus on
the effects of macronutrients on body
composition.
We have also examined the effects of
very low–carbohydrate diets on body
composition in normal-weight men
is to decrease percentage body fat by (19). Twelve healthy normal-weight
simultaneously decreasing fat mass and THE CASE FOR LOW men switched from their habitual diet
increasing lean body mass. Beyond the CARBOHYDRATE DIETS TO
well-characterized favorable effects on ENHANCE BODY COMPOSITION
KEY WORDS:
general health, a lower body fat is A common, albeit inaccurate, axiom in
desirable for athletes to increase mus- nutrition is that a calorie is a calorie (i.e., diet; resistance exercise; carbohydrate;
cular force to body weight ratio and the distribution of macronutrient has body composition
42 VOLUME 32 | NUMBER 1 | FEBRUARY 2010 Copyright Ó National Strength and Conditioning Association
(48% carbohydrate) to a ketogenic diet
(12% carbohydrate) for 6 weeks, and
8 men served as controls consuming
their normal diet. Fat mass, assessed by
dual energy x-ray absorptiometry, was
significantly decreased (23.4 kg) and
lean body mass significantly increased
(1.1 kg) after the ketogenic diet. There
was a significant decrease in serum
insulin (234%), and 70% of the vari-
ability in fat loss on the ketogenic diet
was accounted for by the decrease in
serum insulin concentrations.
In addition to experimental demon-
strations of its efficacy, the importance
of carbohydrate restriction rests on the
fundamental idea that carbohydrate
is more than an energy source. In
distinction to strategies based on re- Figure 1. Fat breakdown as a function of insulin levels. Small reductions in insulin
duction in dietary fat, the rationale for within the physiological range are associated with a large increase in
reduction in dietary carbohydrate de- lipolysis. Adapted from Jensen et al. (6).
rives from basic mechanisms. Carbo-
hydrate is the major stimulus of insulin
and, beyond its role in providing lipolysis several-fold, the response carbohydrate, beyond its role as a
a source of energy, serves as a control being virtually immediate. Insulin also source of energy, has an important
element, either directly via glucose or stimulates lipogenesis by increasing regulatory function in the control of
fructose or indirectly through the glucose uptake and activating lipogenic body fat levels.
effects of insulin and other hormones. and glycolytic enzymes. Small reduc- In skeletal muscle, insulin also has
It is difficult to attribute metabolic tions in insulin levels, such as that anabolic effects by increasing amino
responses and clinical outcomes to one easily achieved with dietary carbohy- acid uptake and protein synthesis and
class of nutrients, but as a principle, one drate restriction, remove the normal inhibiting protein breakdown (17). In-
has to consider the inextricable link inhibition on fat breakdown. Thus,
sulin is generally accepted as a stimula-
between dietary carbohydrate and the low-carbohydrate diets are associated
tor of protein synthesis only when
appearance of plasma glucose and with significant changes in lipid me-
adequate amino acids are available (7),
insulin as an important modulator of tabolism, favoring decreased storage
thus dietary carbohydrates alone are
cellular function. and increased breakdown and oxida-
not a potent stimulus for increasing
tion of fat as well as improvement in
protein synthesis (1,18). However,
INSULIN PHYSIOLOGY atherogenic dyslipidemia. The ability
many dietary protein supplements in-
The manifold functions of insulin can of low-carbohydrate intake to inhibit
clude carbohydrate as a way to in-
be summarized as anabolic. Insulin lipogenesis and to bias lipid metabo-
crease insulin and potentially augment
inhibits breakdown and promotes stor- lism toward oxidation would allow for
protein synthesis. While some evi-
age of nutrients. In this way, dietary more effective processing of the in-
dence exists for an additive effect of
carbohydrate–induced increases in cir- gested fatty acid mix. As an example,
protein and carbohydrate provided
culating glucose and insulin levels serve we showed a reduction in plasma
after resistance exercise on protein
as an important control element on saturated fatty acids in the low-carbo-
synthesis (14), other work has shown
metabolism, especially the regulation hydrate arm of a dietary comparison in
that carbohydrate does not augment
of fuel selection between carbohydrate which this group consumed 3 times the
the response induced by protein (8).
and fat. Carbohydrate restriction stim- amount of saturated fat as the low-fat
ulates a unique metabolic state char- arm (2), supporting the premise that Prior work clearly shows that pro-
acterized by increased fat oxidation ingested fat is efficiently used for fuel viding even small amounts of carbo-
and decreased fat synthesis. In fact, rather than stored when carbohydrate hydrate after exercise rapidly decreases
adipose tissue lipolysis is exquisitely is restricted. In summary, the dominant nonesterified fatty acids and induces
sensitive to changes in insulin within hormone regulating metabolic process- a shift from fat to carbohydrate
the physiological range of concentra- ing of dietary fat is insulin, which is oxidation (13). The relatively minor
tions (6) (Figure 1). Small to moderate primarily stimulated by dietary carbo- positive effect of carbohydrate and
decreases in insulin can increase hydrate. It is not surprising that dietary insulin on protein balance should be
Strength and Conditioning Journal | www.nsca-lift.org 43
Effects of Macronutrients on Body Composition
weighed against the more potent protein, and the low-carbohydrate diet greater decreases in insulin. Resistance
effects of carbohydrate ingestion on group consumed 1.6 g/kg protein. training, independent of diet, resulted
inhibition of fat breakdown and fat Both groups significantly decreased in increased lean body mass without
oxidation, which could be counterpro- their total caloric intake by approxi- compromising fat loss in both diet
ductive for decreasing body fat. mately 600 kcal from baseline, with no groups. The most dramatic reduction
significant difference between the 2 in percent body fat was in the low-
treatment groups. After 16 weeks, the carbohydrate diet resistance training
IMPORTANCE OF RESISTANCE low-carbohydrate diet group lost ap- group (25.3%), followed by low-fat resis-
TRAINING
proximately 2.0 kg more body weight tance training (23.5%), low-carbohydrate
Diet alone can improve body compo- diet only (23.4%), and low-fat diet
than the low-fat diet group (mean 6
sition, but the effects are augmented only (22.0%) groups. These data show
SEM: 9.3 6 0.8 kg versus 7.3 6 0.5 kg,
when combined with exercise. Al- for the first time that resistance training
respectively). The addition of an exer-
though resistance training is not a po- is a potent stimulus to protect lean
cise program (5 d/wk walking and
tent stimulus for enhancing fat loss, body mass in men consuming a low-
2 d/wk resistance training) to the
overloading the musculature is neces- carbohydrate diet, while still allowing
low-carbohydrate diet had synergistic
sary to create the anabolic stimulus for for significantly greater fat loss.
results. The low-carbohydrate exercise
muscle fiber hypertrophy. In combina-
group had the largest weight reduction When our work is compared with the
tion with the appropriate nutritional
(11.2%) compared with the low-fat diet findings of Layman et al. (11), a similar
input, resistance training can enhance
group (8.4%). The most favorable pattern and magnitude of change in
the proportion of fat loss during weight
responses in fat mass were seen in body weight are seen across the 4 groups
loss (24). Kraemer et al. (9) showed
that overweight men who consumed the low-carbohydrate diet groups who (Figure 2). The low-carbohydrate diet
a low-calorie, high-fiber, low-fat diet lost an average of 7.3 6 0.8 kg fat mass groups lost more body fat, independent
lost approximately 9.5 kg in 12 weeks. (4.3% relative body fat), whereas the of training, whereas resistance training
Two other groups who consumed the 2 low-fat diet groups lost an average of had a favorable effect on lean body
same diet but added either endurance 5.3 6 0.3 kg fat mass (2.9% relative mass independent of diet. The combi-
training or a combination of endu- body fat). When comparing the 2 exer- nation of a low-carbohydrate diet and
rance and resistance trainings showed cise groups, independent of diet treat- resistance training appears to be addi-
the same weight loss. However, sub- ment, those participants who received tive in the sense that it maximizes fat
jects who made only dietary changes supervised training lost an average of loss while preserving/increasing lean
had a fat loss of 69% of total weight 1.7 kg or 2.2% more than those who body mass. In other words, a low-
loss, whereas subjects who added were less physically active and they carbohydrate diet combined with resis-
endurance training had a fat loss of had greater preservation of lean body tance training produces the greatest
78% of weight loss, and subjects who mass. The combination of a low- reductions in percent body fat.
also added resistance training lost carbohydrate diet and exercise had
almost exclusively fat (97% of weight the most favorable response for both
HEALTH CONSIDERATIONS
loss). Therefore, the addition of weight fat mass and lean body mass (Figure 2),
For more than 3 decades, official recom-
lifting decreased the loss of lean body suggesting this may be a logical effec-
mendations have emphasized reduced
mass to 3%, compared with a 22% loss tive intervention strategy for weight
total fat, saturated fat, and cholesterol
with endurance-only training and loss in middle-aged women.
intake as the primary method to achieve
a 31% loss in muscle with diet only. We performed a similar experiment and maintain a healthy body weight
Although resistance training clearly in overweight/obese men who were (12). The best estimates of nutrient
improves body composition when added placed in a low-fat diet group that intake in the United States indicate that
to a dietary program, the effects of diets restricted fat to less than 25% of energy percent fat intake has declined over the
varying in macronutrients consumed or a very low–carbohydrate ketogenic past 3 decades, with a concomitant
with and without exercise training diet group that reduced carbohydrate increase in carbohydrate intake (20).
have only been investigated in a few to less than 15% energy. Both groups During the same time, obesity and
studies. Layman et al. (11) reported also participated in a resistance training diabetes rates have increased and heart
that a moderate low-carbohydrate diet program (see Practical Applications) disease remains the leading cause of
(38:30:32; percent of carbohydrate to (16). Body composition was assessed death in most industrialized countries
protein to fat) resulted in more favor- using dual energy x-ray absorptiometry (15). The recent report of the massive
able body composition changes than before and after the 12-week program. trial in the Women’s Health Initiative
a low-fat diet (61:18:26; percent of The results were compared with non- can only be described as discouraging
carbohydrate to protein to fat) in training diet only groups. As expected, with essentially no long-term effect on
middle-aged overweight women. The the low-carbohydrate diet group lost weight loss (4) or cardiovascular disease
low-fat diet group consumed 0.8 g/kg more fat, which was associated with (CVD) (5) on a low-fat diet. In the area
44 VOLUME 32 | NUMBER 1 | FEBRUARY 2010
Figure 2. Effects of diet composition with and without resistance training on change in lean body mass and fat mass after 16 weeks
in untrained women (11) and 12 weeks in untrained men (16). RE = resistance exercise.
of weight loss, experiments continue to with the idea that an intolerance to contributing to these favorable results
show that carbohydrate restriction is at carbohydrate (insulin resistance) is an independent of the effects of weight loss.
least as effective as low-fat diets, usually underlying feature of the metabolic
more effective. In addition to weight syndrome, research has shown that a PRACTICAL APPLICATIONS
loss, emerging research is showing that reduction in dietary carbohydrate results Athletes who want to decrease body
carbohydrate-restricted diets are an in global improvement in traditional and fat and improve body composition
effective strategy to improve the meta- emerging markers associated with this should pay particular attention to di-
bolic syndrome (insulin resistance syn- syndrome, particularly the cardiometa- etary carbohydrate intake. In practice,
drome), which represents a group of bolic profile (22,23). Notably, these same there are many ways to restrict carbo-
seemingly disparate physiologic signs results are found even when body hydrate. In our research studies, dietetic
that indicate a predisposition to obesity, weight does not change, demonstrating counseling was focused on lowering
diabetes, and CVD (22). Consistent that there are underlying mechanisms carbohydrate intake to approximately
Table 1
Sample resistance training program for subjects consuming a low-fat and low-carbohydrate diet
Day 1 (mon) (8–10 reps) (120 s rest) Day 2 (wed) (6–7 reps) (180 s rest) Day 3 (fri) (8–10 reps) (120 s rest)
Squat Barbell lunge Squat
Dumbbell lunge Leg curl/leg extension Pull-down
Bench Incline bench One-leg lunge
Pull-down Seated row Upright row
Upright row Shoulder press Bench
Calf exercise Calf exercise Calf exercise
Ab exercise Ab exercise Ab exercise
Ab exercise = abdominal exercise; Reps = repetitions.
Strength and Conditioning Journal | www.nsca-lift.org 45
Effects of Macronutrients on Body Composition
10–15% of total energy, but this level of Prentice RL, Robbins J, Rossouw JE,
Erin E. Quann is Sarto GE, Schatz IJ, Snetselaar LG,
restriction may not be necessary. We
manager of regu- Stevens VJ, Tinker LF, Trevisan M,
have observed favorable effects on body
latory affairs at Vitolins MZ, Anderson GL, Assaf AR,
composition when subjects were in-
Dairy Manage- Bassford T, Beresford SA, Black HR,
structed to consume beef, poultry, fish, Brunner RL, Brzyski RG, Caan B,
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eggs, oils, and heavy cream; moderate Chlebowski RT, Gass M, Granek I,
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