Nutrition Performance - Effects of Macronutrients on Body Composition, Anabolic Hormones and General Health: Best of Research
“Reality is that which, when you stop believing in it, doesn’t go away.” —Philip K. Dick
Long-Term Effects of Atkins Diet
Two studies published in the respected Annals of Internal Medicine provides convincing
evidence that the Atkins diet is at least as effective as a low-fat/high-carb diet in helping people
shed excess lard without harming their cholesterol levels. Dr. William Yancy and coworkers
examined bodyweight, body composition, blood lipid levels and adverse effects over 24 weeks
in 120 overweight, hyperlipidemic persons who were randomly assigned to follow the Atkins diet
or a low-fat, low-cholesterol, reduced-calorie diet. The Atkins diet led to greater weight loss,
reduction in blood triglyceride levels (harmful blood fats that may trigger heart disease) and
increase in the HDL cholesterol (“good” cholesterol) level compared with the low-fat diet.
Further, investigators found that the LDL cholesterol (“bad” cholesterol) level didn’t
change on average, but increased by more than 10 percent from baseline to week 24 in 30
percent of recipients of the Atkins diet who completed the study. In fact, two participants in the
Atkins group dropped out of the study because of concerns about elevated blood lipid levels.
Also, several symptomatic adverse effects occurred more frequently in the Atkins diet group,
including constipation, headache, diarrhea, general weakness, etc. The authors concluded that
over 24 weeks, healthy hyperlipidemic persons who followed the Atkins diet lost more
bodyweight and body fat than did those who followed a low-fat diet. As the authors pointed out,
however, the monitoring of blood lipid levels remains important because a small percentage of
persons may experience some adverse effects.
The second Atkins diet study published in the same issue found similar weight loss in
persons randomly assigned to the Atkins diet or a conventional high-carb/low-fat diet for one
year. However, the Atkins diet group had a direct and more favorable effect on triglyceride
levels, “good” cholesterol levels and blood sugar controls in the smaller subgroup of patients
with diabetes.
In an accompanying editorial, Dr. Walter Willett, from the Harvard School of Public
Health, wrote: “We can no longer dismiss very-low-carbohydrate diets…Dr. Atkins deserves
credit for his observations that many persons can control their weight by greatly reducing
carbohydrate intake and for his funding of trials by independent investigators.”
High Protein/Low Fat Versus Standard Protein/High Fat
When energy intake is matched and fat intake is reduced to about 30 percent of energy,
the replacement of a moderate percentage of energy from carbohydrate with protein has been
shown to enhance fat loss and spare muscle mass. Furthermore, there are numerous studies
reporting greater improvements in blood sugar control, insulin sensitivity and the blood lipid
profile after weight loss with high-protein diets than after a standard-protein diet.
However, a pertinent question is whether, in the context of low-carb diets, the highprotein
or the high-fat diet is better at improving fat loss and health in general. Dr. Natalie
Luscombe-Marsh and colleagues at the University of Adelaide in Australia compared the effects
of two isocaloric diets (that differed in protein and fat content) on weight loss/fat loss, blood
lipids, appetite regulation and energy expenditure after test meals. This was a parallel,
randomized study in which subjects received either a low-fat, high-protein diet or a high-fat,
standard-protein diet during 12 weeks of energy restriction and four weeks of energy balance.
Fifty-seven overweight and obese volunteers completed the study.
The main finding of this study was that the low-fat/high-protein diet and the highfat/
standard-protein diet (high in monosaturated fat) were equally effective at reducing
bodyweight, improving insulin sensitivity and improving heart disease risk factors. So, it’s
becoming increasingly clear that restriction of carbs in a low-fat/moderate-carb diet or highprotein
diet may be beneficial at improving body composition compared to a low-fat/high-carb
diet (i.e., the American Heart Association diet), possibly by reducing insulin levels and thus,
enhancing breakdown of storage fat. Not surprisingly, the experimental diets had no adverse
effects on kidney function, blood pressure or markers of bone turnover.
Muscle Anabolism: Milk Protein Versus Soy Protein
Dr. Stuart Phillips and co-workers at McMaster University in Canada examined how a
protein source affects the processes of muscle protein synthesis (i.e., anabolism) and muscle
protein breakdown (i.e., catabolism) after resistance exercise. Their first study was an acute
examination of how milk versus soy proteins would support protein accretion (i.e., muscle
hypertrophy).
Subjects performed an intense workout on only one of their legs to isolate the effects on
exercise to a single muscle mass. Immediately following exercise, subjects consumed an
isonitrogenous (18.2 grams of protein) and isoenergetic (750 kilojoules) beverage of either lowfat
milk or a beverage containing hydrolyzed (partially pre-digested) soy proteins as a protein
source. The investigators observed that the soy promoted a more rapid and transient
hyperaminoacidemia than milk. Nevertheless, over the ensuing three hours following resistance
training they observed a markedly greater uptake of amino nitrogen following milk consumption.
In other words, milk protein was more effective at supporting muscle protein anabolism.
The second study by Dr. Phillips and colleagues tested their findings of greater postexercise
anabolic response acutely following resistance training in a chronic resistance training
setting. The subjects always exercised at least two hours post-prandial (after eating) and in the
post-exercise period consumed one drink immediately and a second drink one hour later. The
increase in muscle fiber cross-sectional area was slightly greater in the milk-consuming group
than the other two groups, so Dr. Phillips’ short-term findings were borne out when a long-term
comparison was made.
The authors concluded: “Our findings revealed that even when balanced quantities of
total protein and energy are consumed, milk proteins are more effective in stimulating amino
acid uptake and net protein deposition in skeletal muscle after resistance exercise than are
hydrolyzed soy proteins… In young men completing 12 weeks of resistance training (five days
per week) we observed a tendency (P = 0.11) for greater gains in whole body lean mass and
greater muscle fiber hypertrophy with consumption of milk.”
Macronutrients and Testosterone Levels
Testosterone separates the men from the boys. It promotes protein synthesis and
growth of those tissues with androgen receptors. Testosterone effects can be classified as
virilizing and anabolic, although the distinction is somewhat artificial. Anabolic effects include
growth of muscle mass and strength as well as increased bone density. Virilizing effects include
maturation of the sex organs, a deepening of the voice, growth of torso hair and so on.
Dr. Janne Sallinen and co-workers at the University of Jyväskylä in Finland examined
the relationship between macronutrient intake and blood anabolic hormones. In the first part of
this study, blood basal anabolic hormone concentrations and macronutrient intakes were
examined in the total group of subjects. In the second part of the study, a subgroup of five gym
enthusiasts and five physically active non-athletes performed high-volume and high-intensity
heavy resistance training.
The main finding of this study was that the basal testosterone level correlated with
intake of fat (saturated and monounsaturated fatty acids) and negatively with protein, protein/fat,
protein/carbohydrate and carbohydrate/fat ratios. However, when the two groups were
examined separately, the significant relationship between macronutrient intake and testosterone
was noticed in the strength athletes only. No relationship between the biologically active (free)
testosterone or growth hormone and macronutrient intake were observed in this study.
This study also showed that testosterone responses to heavy resistance training may
be influenced by macronutrient intake. Both total testosterone and free testosterone responses
to training were significantly correlated with total fat, saturated fatty acids, monosaturated fatty
acids and negatively with protein, protein/fat, carbohydrate/fat and protein/carbohydrate ratios.
The authors concluded, “The present nutritional data in relation to [blood] basal testosterone
concentration and [blood] total and free testosterone responses to [heavy resistance training]
suggest that the moderate intake of both fat and protein could be recommended for strength
athletes.” In other words, low-fat or very-high-protein intake may have adverse effects on
testosterone levels.
More recently, 39 healthy men were studied while they were consuming a high-fat/lowfiber
diet and after an eight-week modulation switched to an isocaloric low-fat/high-fiber diet.
After diet modulation, blood testosterone concentration fell, accompanied by small decreases in
free (biologically active) testosterone. The authors suggested that the low-fat diet modulates
androgen levels and metabolism, providing an unfavorable environment for the growth and
development of prostate cancer. While this hypothesis makes some sense, they ignored the fact
that low testosterone levels also have adverse effects such as decreased sex drive, poor
erections, lowered sperm count, reduced muscle mass and so on. So, what’s the take home
message? The low-fat diet may be good for your prostate, but it’s not good for your dick and
muscles!
High-Protein Diet Spares Muscle Mass During Energy Restriction
Numerous studies have shown that high-protein diets increase satiety and thus facilitate
fat loss. Furthermore, epidemiologic studies show a significant relationship between increased
protein intake and lower risk of hypertension (high blood pressure) and coronary heart disease.
Also, purported adverse effects of high-protein diets are false or at least greatly exaggerated.
A recent four-month study by Dr. Donald Layman and colleagues examined the
interaction of two diets (high-protein/moderate-carb versus low-protein/high-carb) with exercise
on body composition and blood lipids in women during weight loss. Diets were equal in total
energy and fats, but differed in protein content: 1.6 grams per kilogram of bodyweight per day in
a high-protein group and 0.8 grams per kilogram in a high-carb group. Not surprisingly, subjects
in the high-protein and high-protein plus exercise groups lost more weight and fat and lost less
lean mass than the high-carb and high-carb plus exercise groups. As expected, exercise
promoted fat loss and preserved lean mass, so the combined effects of diet and exercise were
additive for improving body composition. The authors concluded, “This study adds to the
increasing body of evidence supporting protein-sparing (i.e., anti-catabolic) effects derived from
maintaining higher protein intakes during energy restriction.”
High-Protein Diet Improves Weight Management
Dr. MP Lejeune and co-workers at the University of Maastricht investigated whether the
addition of protein to the diet might limit weight regain after a weight loss of five to 10 percent.
One hundred and thirteen overweight subjects followed a very-low-energy diet for four weeks,
after which there was a six-month period of weight management. During weight management,
subjects were randomized into either a protein group (30 grams of protein per day in addition to
their own usual diet) or a control group. The protein group showed a lower weight regain and a
decreased waist circumference. Interestingly, the results also indicated that weight regain in the
protein group consisted of only fat-free mass, whereas the control group gained fat mass as
well.
Low-Glycemic Diet Superior to Conventional Low-Fat Diet
The glycemic index is a ranking of carbs according to the extent to which they raise
blood sugar levels after eating. Foods with a high-glycemic index are those which are rapidly
digested and absorbed and result in marked fluctuations in blood sugar levels. Glycemic load
builds on the glycemic index to provide a measure of total glycemic response to a meal
(glycemic load=glycemic index [percent] x grams of carbohydrate per serving).
In a study by Dr. LaHaye and co-workers at the Queen´s University in Canada, 120
subjects who were advised to follow a low-glycemic load diet were evaluated and compared
with 1,434 patients who were advised to follow the principles of “Canada's Food Guide to
Healthy Eating.” As expected, the investigators found that the low-glycemic diet was superior to
the “healthy eating” diet:
ı Subjects on the low-glycemic diet lost more weight at six months: 2.8 kilograms (2.2
pounds=1 kilogram) lost versus 0.2 kilograms gain.
ı The low-glycemic diet group had a greater reduction in abdominal lard: 2.9 centimeters
versus 0.4 centimeters.
ı Subjects on the low-glycemic diet had a greater improvement in good cholesterol (HDL)
high-density lipoprotein cholesterol, triglycerides and blood sugar control.
ı After one year of follow-up, the low-glycemic load subjects had maintained or even
augmented the initial results.
In sum, it’s now clear that the conventional high-carb/low-fat diet is far form the ideal
diet. Although Dietary Guidelines for Americans 2005 gives greater emphasis on increased
consumption of whole grains rather than refined grains, this is unlikely to improve daylong blood
sugar control because many so-called whole-grain products produce as much postprandial
glycemia as do their white flour counterparts. University of Sydney´s glycemic index website
(http://www.glycemicindex.com) gives the following sensible recommendations to decrease
glycemic load:
ı Use breakfast cereals based on oats, barley and bran.
ı Reduce the amount of potatoes you eat.
ı Enjoy all types of fruit and vegetables (except potatoes).
ı Eat plenty of salad vegetables with vinaigrette dressing.
Very-Low-Carb Diet is Very Effective for Fat Loss
A randomized, balanced, two-diet study by Dr. Jeff Volek and colleagues at the
University of Connecticut compared the effects of an isocaloric, energy-restricted, very-low-carb
diet (ketogenic diet) and high-carb/low-fat diet on weight loss and body composition in
overweight/obese men and women. Despite significantly greater calorie intake (1,855 versus
1,562 kcalories per day), both the between and within group comparison revealed a distinct
advantage of a very-low-carb diet over a low-fat diet for weight loss/fat loss for men. In fact, five
men showed more than 10 pounds difference in weight loss. The majority of women also
responded more favorably to the ketogenic diet, especially in terms of trunk fat loss.
Furthermore, the individual responses revealed that three men and four women who did the
ketogenic diet first, regained body mass and fat mass after the switch to the low-fat, whereas no
subjects regained weight or fat mass after switching to the ketogenic diet.
In conclusion, a calorie is certainly not a calorie. A very-low-carb diet indeed provides a
"metabolic advantage" and a greater weight-loss/fat-loss-per-calorie-consumed compared to
isocaloric high-carb diet. In fact, this study suggests that calorie content may not be as
predictive of fat loss as is reduced carbohydrate consumption. If you want to read all the details,
the free full-text paper of Volek study is available at www.nutritionandmetabolism.com
Very-Low-Carb Diet and Muscle Anabolism
One of the most enduring urban legends in the nutrition world is that low-carb intake
leads to progressive loss of muscle mass (muscle protein). Fortunately, the human body is way
smarter than some nutrition “experts.” True, animals share the metabolic deficiency of the total
(or almost total) inability to convert fatty acids to glucose (blood sugar). So, the primary source
for a substrate for gluconeogenesis (the formation of glucose from non-carbohydrate molecules)
is amino acid, a building block of protein, with some help from glycerol from fat tissue
triglycerides (i.e., storage form of fat; contains one glyceride molecule plus three fatty acid
molecules).
However, when the rate of mobilization of fatty acids from fat tissue is accelerated, as,
for example, during a very-low-carb diet, the liver produces ketone bodies. The liver can’t utilize
ketone bodies and thus, they flow from the liver to extra-hepatic (outside of the liver) tissues
(e.g., brain, muscle) for use as a fuel. Simply stated, ketone body metabolism by the brain
displaces glucose utilization and thus spares muscle mass. In other words, the brain derives
energy from storage fat during a very-low-carb diet.
A well-controlled study by Dr. Jeff Volek and colleagues examined the effects of a sixweek,
very-low-carbohydrate diet body composition. Interestingly enough, their results indicated
that fat mass was significantly decreased (-3.4 kg) and lean body mass significantly increased
( 1.1 kg). As expected, a very-low-carbohydrate diet led to significant decrease in blood insulin
concentrations and there was a significant correlation between the decrease in insulin and the
decrease in body fat, indicating that fat tissue breakdown was up-regulated, which was also
supported by the elevated ketone body levels.
More recently, a study by Dr. Harber and co-workers at the University of Michigan
examined the influence of a very-low-carb/high-protein diet on skeletal muscle protein synthesis
(i.e., anabolism) and whole-body protein degradation. Eight healthy subjects volunteered for
participation in this study. After being admitted to the hospital, the subjects ate a standardized
diet for two days consisting of 60 percent of total energy from carbs, 30 percent from fat and 10
percent from protein. During week one of a very-low-carb/high-protein diet, the subjects
consumed a weight-maintaining diet consisting of five percent of total energy from carbs, 60
percent from fat and 35 percent from protein.
The main finding of this study was that the skeletal muscle protein synthesis increased
despite strict carb restriction and a dramatic reduction in insulin levels. However, the increase in
skeletal muscle anabolism was accompanied by an increase in whole-body protein degradation.
So, what’s the take home message of this study? Well, it confirmed that a very-low-carb/highprotein
diet certainly doesn’t lead to progressive loss of muscle mass. However, this study also
suggests that a very-low-carb diet isn’t ideal if your primary goal is to increase muscle mass, as
the study indicated that the increase in muscle anabolism was accompanied by an increase in
whole-body protein breakdown.
Finally, a recent study at the Ball State University examined how carbohydrate status
may affect stimulation of anabolic signalling pathways in response to resistance exercise in
human skeletal muscle. In this study, experienced cyclists performed 30 repetitions of knee
extension exercise at 70 percent of one repetition maximum after a low- (two percent) or high-
(77 percent) carbohydrate diet, which resulted in low or high pre-exercise muscle glycogen
content. According to the authors of this study, “The present findings suggest that…exercising
in a glycogen-depleted or malnourished state may disrupt mechanisms involved with protein
translation through the AKT pathway. In this manner, adaptations to an acute bout of exercise
may be blunted.”
Long-Term Comparison of Popular Weight Loss Diets
Dr. McAuley and colleagues at the University of Otago in New Zealand reported a
randomized trial comparing very-low-carb/high-fat (no more than 20 grams of carbs per day)
and high-protein diets (“Zone”) with the conventional high-carb/low-fat approach (at least 55
percent of total energy from carbs). A total of 93 overweight women received advice following
randomization to very-low-carb, Zone, or high-carb/low-fat dietary regimes, to achieve weight
loss followed by weight maintenance over 12 months.
After six months, both “alternative diets” (i.e., very-low-carb and Zone) had several
advantages when compared to the conventional high-carb/low-fat diet. Reductions in body fat,
waist circumference and harmful blood lipids were all greater in those on the high-protein and
high-fat diet than those recommended the high-carb/low-fat diet. Despite the initial
improvements in the very-low-carb group, during the final six months, this group had an
increase in fat mass and waist circumference, which was greater than the increase seen in the
Zone and high-carb/low-fat groups. However, those following the Zone diet had a particularly
favorable outcome; the improvements were largely maintained so that at 12 months, weight and
fat mass were around six and four kilograms lower than at baseline.
According to the authors, “This study provides strong support for the use of high-protein
diets as an alternative to the conventional approach. Bodyweight, fat mass and several major
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