Sports Med 2005; 35 (1): 1-9

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Diet and Exercise for Weight Loss

A Review of Current Issues
Jeff S. Volek, Jaci L. VanHeest and Cassandra E. Forsythe
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs,
Connecticut, USA

Abstract Obesity is a fast growing epidemic that is primarily due to environmental

influences. Nutrition and exercise represent modifiable factors with a major
impact on energy balance. Despite considerable research, there remains continued
debate regarding the energy content and the optimal macronutrient distribution for
promoting healthy and effective weight loss. Low-fat diets have been advised for
many years to reduce obesity. However, their effectiveness has been recently
challenged, partly because the prevalence of obesity continues to rise despite
reductions in fat intake. There are also concerns regarding the methodology of
clinical trials showing benefits of fat reduction on weight loss. Although often
viewed as a fad diet, very low-carbohydrate (ketogenic) diets are very popular and
several recent clinical trials indicate they are more effective at promoting
short-term weight loss and improving characteristics of the metabolic syndrome
than low-fat diets. However, there is a need to obtain long-term safety and
efficacy data. Clearly, weight loss can be achieved with a variety of diet interven-
tions but the effects on other health-related aspects also need to be considered and
studied in more detail. Exercise can have positive effects on weight loss, weight
control and overall general health, although debate exists concerning the most
effective mode, duration and intensity of exercise required to achieve these
effects. Importantly, any effective weight control treatment must consider a
life-long plan or there will likely be weight regain. Perhaps the most challenging,
but rewarding, question that faces researchers is how to predict individual
responses to diet and exercise interventions.

There has been a rapid increase in obesity in the nent lifestyle changes are made. Weight loss should
US, which cannot be totally explained by genetic not be the sole endpoint by which the effectiveness
factors,[1] highlighting the importance of environ- of a particular treatment is assessed. Effective inter-
ment or lifestyle choices as causative factors. In- ventions should also consider the impact on the
creased energy intake and a sedentary lifestyle re- composition of weight loss (e.g. ratio of lean and fat
present the major targets for interventions aimed at tissue), regional location of the weight loss (e.g.
combating this epidemic. A large body of literature peripheral vs central), measures of physical per-
exists on the effects of diet and exercise with no formance (e.g. muscular strength, power and endur-
clear agreement among researchers on their short- or ance, cardiorespiratory fitness), activities of daily
long-term efficacy. Many combinations of diet and living, how a particular intervention affects mental
exercise can produce weight loss, but if treatment is health and most importantly risk for disease (e.g.
stopped, weight is regained. In this sense, over- diabetes mellitus, coronary artery disease, hyperten-
weight is not curable, but it is manageable if perma- sion). In this paper, we briefly discuss the role of
2 Volek et al.

energy content and then overview the controversial, Importantly, long-term retention of weight loss
but pertinent, issue of fat restriction versus carbohy- following an increased rate of initial weight loss
drate restriction on weight loss and weight control. must be accompanied by continued treatment that
The role of exercise is also summarised. We will not may consist of regular exercise, diet education and
discuss dietary supplements, pharmacological or behavioural therapy, otherwise, significant weight
surgical treatments of obesity for which the reader is regain is likely.[10] Although the concept of inducing
encouraged to consult other excellent reviews.[2] a greater initial rate of weight loss to enhance long-
term weight maintenance challenges conventional
1. Diet and Weight Loss wisdom, some evidence exists to support this hy-
pothesis. Hypothetically, a greater rate of initial
Weight reduction requires that energy expendi- weight loss could have psychological benefits by
ture exceed dietary energy intake. Despite a consid- enhancing initial motivation, but this has not been
erable amount of research dedicated to understand- adequately evaluated. The health effects of this ap-
ing the role of diet in mediating weight control, there proach have also not been adequately addressed, in
remains disagreement regarding basic issues includ- particular, how the rate of weight loss affects body
ing the appropriate energy content, and perhaps composition or regional fat loss.
more controversial, the ideal macronutrient distribu-
tion. 1.2 Macronutrient Composition

1.1 Energy Content Research is far from clear in determining the

ideal macronutrient distribution for weight loss and
Manipulation of the energy content will impact weight maintenance and the safety/efficacy and ad-
the rate of weight loss. Very low-calorie diets will vantages/disadvantages of the diverse approaches to
result in larger, more rapid reductions in weight loss, weight control promoted in the lay press. Commer-
whereas a small to moderate reduction in energy cial weight-loss diets vary from ultra low low-fat
intake will result in a small, steady rate of weight (Ornish; Pritikin) to ultra low-carbohydrate (Atkins)
loss. The pertinent question becomes: does the rate and everything in between. Among researchers, the
of weight loss affect long-term weight maintenance area given the most attention is restriction of dietary
or other health-related outcomes? fat and currently this approach has been challenged
Although it is commonly recommended to with the resurgence of very low-carbohydrate diets.
achieve a slow, steady rate of weight loss to enhance Here we discuss the diametrically opposed low-fat
long-term weight maintenance, this notion is not and very low-carbohydrate diets.
supported by all research.[3] Analyses of several
weight-loss intervention studies have indicated that 1.2.1 Dietary Fat
greater rate of initial weight loss is positively associ- This question is a widely debated topic among
ated with sustained weight loss up to 5 years lat- weight-loss researchers.[11-13] Those who argue
er.[4-9] A cause and effect relationship cannot be against a role of fat restriction in obesity manage-
made from these types of studies but it does provide ment often site that the percentage fat intake in the
relevant information that could have important im- US has decreased at the same time the prevalence of
plications on prescription of energy content. In a obesity has dramatically increased,[14,15] yet this can-
randomised clinical trial, subjects who were pre- not be used as a sole argument because other factors
scribed a very low-energy diet for 8 weeks lost the may explain this trend such as greater physical inac-
same amount of weight as a group prescribed a tivity. Those in favour of targeting fat restriction
moderate energy diet for 17 weeks. Data obtained point to the greater caloric density of fat and argue
after 1- and 2-year follow-up testing indicated that high-fat diets favour passive and active over con-
subjects consuming the very low-energy diet who sumption of energy.[16] In support of fat restriction
lost the weight faster maintained the weight loss as being important for weight maintenance, observa-
slightly better than the group who lost weight at a tional data from the National Weight Control Regis-
slower rate.[9] try has shown that individuals who maintained an

 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Diet and Exercise for Weight Loss 3

average weight loss of ~13.6kg for an average of 5.5 could be counterproductive and, therefore, current
years are consuming a low-fat diet (~24% of energy dietary recommendations for these people may need
from fat) and expending approximately 11830 kJ/ to be modified.[38,39]
week through physical activity.[17] Despite the im-
Another issue not adequately addressed in previ-
portance of this issue, surprisingly few randomised
ous research is whether fat restriction affects the
clinical trials have examined the impact of diets
composition of weight loss. In a meta-analysis, Gar-
differing in macronutrient composition on weight
row and Summerbell[40] predict from regression
loss and maintenance.
analysis that for a weight loss of 10kg by dieting
Two recent meta-analyses both concluded that a alone the expected loss of fat mass is 71% and when
reduction in dietary fat in an ad libitum diet facili- a similar weight loss is achieved by both diet and
tates weight loss.[3,18] In their review of 28 clinical endurance exercise the expected loss from fat mass
trials mainly of short duration, it is estimated that a is increased to 83%. Whether fat restriction per se
reduction of 10% in the proportion of dietary fat affects the composition of weight loss was not spe-
results in a reduction in weight of 16 g/day or a cifically addressed in the meta-analysis, but there is
5.8kg advantage if carried out to 1 year.[18] Willett[13] some indication that composition of weight loss
has criticised the interpretation of these meta-analy- might be more favourable with a diet higher in
ses arguing that serious flaws exists in many of the protein or lower in carbohydrate. Layman et al.[41]
included studies because the control groups did not showed similar weight loss after 10 weeks of dieting
receive comparable treatment (diet advice and moti- in overweight women who consumed a diet of 30%
vation), thus biasing a favourable outcome for fat protein, 41% carbohydrate and 19% fat versus an
reduction. Based primarily on results of four studies isoenergetic diet 16% protein, 58% carbohydrate,
that included an adequate control group that re- and 26% fat. However, the higher protein and lower
ceived an intervention,[19-22] Willett[13] concludes carbohydrate diet resulted in significantly greater
that fat restriction per se does not enhance long-term
loss of fat and retention of lean body mass. In
(1 year or longer) weight loss or prevent regain of
support of higher protein intake, fat loss was greater
weight.
after 6 months of a high-protein versus a high-
To complicate the issue even further, the effec- carbohydrate diet (both diets were equal in fat).[42]
tiveness of fat reduction must be considered along Higher protein intake has also been shown to result
with the effect on other health-related outcomes and in better weight maintenance after weight loss.
body composition. There is overwhelming evidence There is a need to perform more studies that directly
that low-fat diets are effective in reducing total compare diets of different macronutrient distribu-
cholesterol and low-density lipoprotein-cholesterol tion; however, the limited data indicate that diets
(LDL-C).[23] There is concern, however, that low- lower in carbohydrate and higher in protein may
fat/high-carbohydrate diets may increase risk for offer some benefit. Since accumulation of fat in the
heart disease by increasing triglyceride and re- abdominal area is associated with insulin resistance,
ducing high-density lipoprotein-cholesterol (HDL- diabetes, dyslipidaemias and atherosclerosis,[43] diet
C) levels,[24-26] a problem particularly relevant for studies should measure fat loss in this region.
people with the metabolic syndrome. Well con-
trolled feeding studies indicate that low-fat/high- The public has been advised to restrict fat intake
carbohydrate diets exacerbate these lipid responses for over 30 years with the primary justification to
when not associated with significant weight loss or reduce obesity. Yet, it has been argued whether
increased physical activity.[23,27] Low-fat/high-car- these recommendations were based on ‘hard’ sci-
bohydrate diets have unfavourable effects on fasting ence,[44] so the debate continues. Clearly, further
triglycerides,[28,29] postprandial lipaemia,[30-32] HDL- comparative research with appropriate control
C,[33-35] and size and composition of LDL-C.[36,37] groups that consider the associated health-related
Thus, in individuals with characteristics of the meta- outcomes is needed to answer the question whether
bolic syndrome, restricting fat to very low levels fat reduction is beneficial for weight control.

 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
4 Volek et al.

1.2.2 Low-Carbohydrate Diets tribution with the same energy content. Very low-
At the opposite end of the macronutrient distribu- carbohydrate diets result in powerful metabolic ad-
tion spectrum are very low-carbohydrate diets, aptations to enhance mobilisation and utilisation of
which by nature tend to be very high in fat. There lipids while sparing carbohydrate fuel sources.[50,51]
has been a resurgence of diets promoting a low- A metabolic advantage driven by increased protein
carbohydrate intake, perhaps due to the allure of fad turnover to fuel gluconeogenesis[52] is a plausible
diets or more likely their greater weight reducing hypothesis to explain greater weight loss on very
potential. Regardless of the reason for their popular- low-carbohydrate diet compared with a low-fat di-
ity, the recent findings of several randomised et.[53] Very-low carbohydrate diets suppress appetite
clinical trials comparing very low-carbohydrate and and ad libitum energy intake,[54] which may be par-
low-fat diets from independent laboratories requires tially due to the fewer food choices available on the
that this ‘non-conventional’ diet approach be con- diet, but a more likely explanation is the inhibitory
sidered as a viable treatment for weight loss. effects of the primary circulating ketone body,
There were several studies performed in the 3-hydroxybutyric acid,[55] on appetite.
1960s and 1970s that showed greater weight loss Some early reports show that very low-carbohy-
with a very low-carbohydrate compared with a low- drate diets resulted in preferential loss of fat and
fat diet, even when diets contained the same energy preservation of lean body mass.[56-60] In agreement,
content,[45] suggesting “a calorie is not a calorie” we recently reported that a free-living 6-week very
and, therefore, indicative of metabolic advantage. low-carbohydrate diet resulted in significant de-
Metabolic advantage in this sense is defined as a creases in fat mass and increases in lean body mass
greater weight loss with a very low-carbohydrate in normal-weight men.[60] In a follow-up study, we
diet compared with a low-fat diet of equal energy showed that a very low-carbohydrate diet resulted in
content. Very little follow-up work was done until 2-fold greater whole body fat loss and 3-fold greater
recently as evidenced by several recent randomised fat loss in the trunk region compared with a low-fat
clinical trials again showing greater weight loss with diet.[61] Although the mechanisms by which very
very low-carbohydrate diets ranging from 3 to 12 low-carbohydrate diets increase fat loss have not
months in duration.[46-49] Weight loss in these studies been elucidated, a reduction in insulin is probably
was on average 2-fold greater in subjects following important in explaining a portion of the greater fat
the very low-carbohydrate compared with low-fat loss.[60] Inhibition of lipolysis occurs at relatively
diet. Since food was not provided in these studies, it low concentrations of insulin with a half-maximal
is possible less energy was consumed during the effect occurring at a concentration of 12 pmol/L and
very low-carbohydrate diet, but energy intakes were a maximal effect at a concentration of about
similar between diets according to analysis of re- 200–300 pmol/L.[62] Thus, even small reductions in
ported intakes. insulin may be permissive to mobilisation of body
Metabolic advantage is proclaimed to be a viola- fat on a very low-carbohydrate diet.
tion of the first law of thermodynamics and mistak- Much of the concern regarding very low-carbo-
enly used to support the notion “a calorie is a calo- hydrate diets is related to potential adverse effects
rie” or that the macronutrient distribution does not on heart disease. Studies have repeatedly shown that
influence weight loss independent of energy con- short-term very low-carbohydrate diets up to 1 year
tent. However, diets very low in carbohydrate utilise do not adversely affect risk factors for cardiovascu-
different chemical pathways that vary in efficiency, lar disease.[46-49,57] Studies consistently show that
thus weight loss can indeed vary compared with an very low-carbohydrate diets reduce fasting triacylg-
isoenergetic low-fat diet without violating the first lycerols and postprandial lipaemia by 30–55%,
law of thermodynamics. In other words, there can be which is associated with significant increases in
and are differences in energy expenditure associated HDL-C, decreases in total cholesterol/HDL-C ratio
with the metabolism of different macronutrients, and a shift to a larger LDL particle distribution.[63-67]
which could explain some of the differences in Insulin levels are also decreased and glucose is
weight loss on diets of different macronutrient dis- normalised. These beneficial effects are independent

 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Diet and Exercise for Weight Loss 5

of weight loss and tend to be more pronounced in energy stores = energy intake – energy expenditure)
individuals with the metabolic syndrome. is also important in the process of weight reduction
The metabolic syndrome is a highly prevalent and/or weight maintenance. Organised physical ac-
multifaceted clustering of cardiovascular disease tivity is one component of energy expenditure that
risk factors with key features of central obesity, can be altered significantly. It is important to consid-
insulin resistance, dyslipidaemia and hypertension, er several factors when prescribing physical activity
as well as chronic inflammation, procoagulation and as a weight loss technique such as: (i) type or mode
impaired fibrinolysis.[68-70] Although the precise def- of activity; (ii) duration of the activity; and (iii)
inition varies, it is estimated that almost 25% of intensity of the exercise. Each of these components
adults aged >20 years and 40% of adults aged >40 can be altered independently with different overall
years have metabolic syndrome in the US[71] and, responses by the individual.
therefore, it has been described as a healthcare crisis The mode of activity can range from lifestyle
of epidemic proportions.[72] The basis of therapies at activities (e.g. gardening or mowing the lawn) to
this time are interventions promoting weight loss specific exercises (e.g. running, swimming or
and physical activity,[73] but diet represents another weightlifting). Lifestyle activities appear to be use-
behavioural aspect that could have an important ful for weight loss when coupled with dietary inter-
impact on the risk factors associated with metabolic vention.[77,78] These activities must be carefully ex-
syndrome. The dyslipidaemia of metabolic syn- amined in light of the intensity demands of the
drome includes increased fasting and postprandial activity, with more physically demanding activities
triacylglycerols, low HDL-C and a predominance of providing the greatest results.
small LDL particles. As overviewed in the para- Resistance training is gaining acceptance as a
graph above, these lipid disorders are all improved useful tool in weight reduction interventions. This
on a very low-carbohydrate diet in addition to glu- form of training has been thought to increase fat-free
cose and insulin, even without weight loss. Thus, mass resulting in improved resting energy expendi-
carbohydrate restriction should be looked at as a ture.[79,80] Although various intervention studies
viable treatment approach for metabolic syndrome. have been completed, the data do not suggest the use
Although the benefits of following a very low- of resistance training either alone or an adjunct to
carbohydrate, moderate protein and fat diet on fat endurance training and dietary intervention for en-
loss look promising, they remain controversial[74,75] hanced weight loss.[79,80] However, other factors
and long-term (>1 year) data on their safety and must be considered regarding resistance training.
efficacy are not available at this time. Decreased Enhanced strength gains should increase the ability
appetite may work in concert with a metabolic ad- of the overweight individual to perform other tasks
vantage to facilitate weight loss on a very low- (i.e. daily living tasks or physical activity), thereby
carbohydrate diet. Although adverse effects have increasing the likelihood of success in overall
not been observed in clinical trials, very low-carbo- weight reduction strategies.
hydrate diets may not be advisable for individuals The effect of exercise intensity on weight loss has
with a history of gout and there is concern the diet been studied recently in large-scale interventions.
may increase the renal acid load and, therefore, Various methods have been employed to assess or to
exacerbate the risk of kidney stones and osteo- prescribe exercise intensity such as a percentage of
porosis.[76] Further long-term work examining these maximal heart rate or a percentage of maximal oxy-
issues is of high priority as a large percentage of the gen consumption (V̇O2max). The exercise habits of
public continue to follow a low-carbohydrate ap- individuals in the US National Weight Loss Registry
proach. were assessed. The individuals spent at least one-
quarter of their exercise time in vigorous physical
2. Exercise and Weight Loss
activity.[17] A more recent study by Jakicic and
Section 1 focused on the use of dietary interven- colleagues[81] evaluated various combinations of in-
tions in weight reduction or weight management. tensity and duration on weight loss in overweight
The other half of the energy balance equation (∆ women. Females were placed into one of four

 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
6 Volek et al.

groups: (i) vigorous intensity and high duration; (ii) less effective than >150 minutes per week at causing
moderate intensity and high duration; (iii) vigorous weight loss.[85] Based solely on the energy balance
intensity and moderate duration; or (iv) moderate equation, increased duration of exercise should re-
intensity and moderate duration. All combinations sult in greater weight loss (assuming energy intake
of intensity and duration caused significant weight remains fixed). The literature on weight loss and
loss; however, no differences were reported between weight management supports this claim. Although
the types of intervention.[81] One reason for the the literature remains controversial regarding the
findings was that the potential for total energy ex- benefits of exercise on bodyweight loss, physical
penditure between the groups was smaller than pro- activity is the primary factor impacting bodyweight
posed resulting in an inability to differentiate be- maintenance. It is important to utilise the guidelines
tween the exercise stimulus in this study. Generally, described above to maintain weight loss over ex-
the data supports the need for sufficient duration of tended periods of time.
moderate intensity exercise (55–70% maximal heart Public health recommendations and the current
rate) for weight loss. findings from intervention studies support the use of
An additional aspect of intensity is often over- longer (200–300 minutes per day or greater) dura-
looked when prescribing weight loss interventions – tions of activity.[84] The ability of individuals to
substrate oxidation. The intensity of the activity develop habitual exercise behaviours is critical in
should relate to the fuel sources utilised during the long-term weight maintenance. It is important to
exercise with higher intensity exercise using prima- provide exercise recommendations that are reasona-
rily carbohydrates as a fuel and lower intensity using ble from a behavioural perspective. Recent epidemi-
primarily fats as a fuel. However, Melanson et al.[82] ological studies report a 1.8–2.0kg average annual
reported no difference in 24-hour substrate oxida- weight gain for US adults.[86] Hill and colleagues[86]
tion following either a bout of exercise at 40% or suggest small weekly increases in physical activities
70% V̇O2max. In addition, there were sex differences such as walking 1.6km (1 mile) per day. Walking
in substrate oxidation in response to the exercise 1.6km is approximately 2000 steps and would result
interventions with females oxidising a higher pro- in a caloric expenditure of 100–150 kcals. The addi-
portion of fat compared with their male counter- tion of walking to small changes in dietary intake
parts. Melanson et al.[82] refute the notion that low- (~100 kcal/day) would result in weight maintenance
intensity exercise facilitates enhanced fat utilisation for the average person. An additional 2000 steps per
following exercise, although the low-intensity exer- day (or 1.6km of walking) is a very mild interven-
cise is higher in fat oxidation during the exercise tion strategy that is easily obtainable and could be
bout than the higher intensity exercise. Current un- effective from a behavioural standpoint.
derstanding of the impact of exercise intensity on
substrate oxidation remains unclear. During bouts of 3. Conclusions
equivalent total energy expenditure, the intensity of As the prevalence of overweight and obesity
the exercise does not directly relate to the absolute continues to rise in adolescents and adults, there is
volume of fat oxidised. Further research is necessary an urgent need to enhance our understanding of how
in this area to more clearly delineate the influence of modifiable treatments including diet and exercise
exercise intensity, in the context of total caloric affect short- and long-term weight loss and other
expenditure associated with activity. health-related outcomes. Collectively, research sup-
Current guideline recommendations suggest 30 ports the concept that a diet of any macronutrient
minutes of physical activity, 5 days per week.[83,84] composition can lead to short-term weight loss; so
This recommendation has been effective in reducing the more pertinent question becomes is there a spe-
the risks for health-related problems such as diabe- cific dietary approach that is more effective at main-
tes or cardiovascular disease. The 150-minute week- taining weight loss long-term, or perhaps more im-
ly dose of activity has not been supported in the portantly, is there a diet that results in improved risk
weight-loss literature. Studies investigating varied status for disease? Low-carbohydrate and low-fat
durations found that ~150 minutes per week was diets each have advantages and disadvantages in

 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (1)
Diet and Exercise for Weight Loss 7

terms of their impact on risk for disease and there is surgical treatment of obese female monozygotic twins. Obes
Surg 1999 Jun; 9 (3): 265-8
a great deal of variation in the individual response to 7. Jeffrey RW, Wing RR, Mayer RR. Are smaller weight losses or
these diets. There is also evidence that diets higher more achievable weight loss goals better in the long term for
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low fat, high carbohydrate diet v fixed energy intake. BMJ
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same diet. Future work focusing on methods to past 25 years of weight loss research using diet, exercise or diet
plus exercise intervention. Int J Obes Relat Metab Disord 1997
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importance of exercise is less controversial, but few fat diets in body weight control: a meta-analysis of ad libitum
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one important issue pertains to the question of what 83-90
is the minimum effective dose to achieve health 13. Willett WC. Dietary fat plays a major role in obesity: no. Obes
benefits. From a public health perspective, it seems Rev 2002 May; 3 (2): 59-68
14. Kuczmarski RJ, Flegal KM, Campbell SM, et al. Increasing
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JAMA 1994; 272: 205-11
against excessive exercise). Strength training is en- 15. From the Centers for Disease Control and Prevention. Daily
couraged to specifically enhance lean body mass dietary fat and total food-energy intakes: NHANES III, phase
and force production capabilities. Individual pre- 1, 1988-91 [letter]. JAMA 1994; 271: 1309
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19. Jeffery RW, Hellerstedt WL, French SA, et al. A randomized
Acknowledgements trial of counseling for fat restriction versus calorie restriction
in the treatment of obesity. Int J Obes Relat Metab Disord 1995
Jeff S. Volek has received funding from Natural Alterna- Feb; 19 (2): 132-7
tives International, Dairy Management Incorporated and the 20. National Diet-Heart Study Research Group. The National Diet-
Robert C. Atkins Foundation to conduct research related to Heart Study final report. Circulation 1968; 18: 1-154
diet and exercise on weight loss and/or body composition. 21. Knopp RH, Walden CE, Retzlaff BM, et al. Long-term choles-
terol-lowering effects of 4 fat-restricted diets in hypercholes-
terolemic and combined hyperlipidemic men: the Dietary Al-
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