the effects of a low carbohydrate diet on health risk ......described in dr. atkins’ diet...
TRANSCRIPT
The Effects of a Low Carbohydrate Diet on
Health Risk Factors, Weight Loss, and Compliance
Health Promotion and Disease Prevention Symposium
May 6, 2003
Leonard Armstrong, Lily Chiang, Christopher Cox, Grace Kao, Jason
Keune, Carol Lin, William McCoy, Terri McMillan, Gita Mody, Craig Press, Thomas Shane, Celaine So, Benjamin Tollefsen
The February 2003 issue of Men’s Fitness magazine dubbed St. Louis as the nation’s
fifth fattest city, trailing only Houston, Chicago, Detroit, and Philadelphia. The number of
overweight and obese people is not only large in St. Louis but is growing throughout the country.
Although being overweight or obese used to be considered mostly a cosmetic problem, it has
become obvious that weighing too much can cause medical complications. This report aims to
consider the efficacy of a low carbohydrate diet on health promotion and weight loss.
We all have images of what it means to be overweight or obese. Clinically speaking,
though, a person’s weight classification is based on his or her Body Mass Index, or BMI. Body
mass index is calculated as weight in kilograms divided by the square of height in meters
(kg/m2). For an adult, overweight is defined as a BMI greater than or equal to 25.0 kg/m2 and
obese is defined as a BMI greater than or equal to 30.0 kg/m2.
So how bad of a problem is overweight and obesity in the United States? The most
recent data show that the prevalence of obesity in 1999-2000 was 30.5% while the prevalence of
overweight during this time period was 64.5%. Thus, almost two thirds of all Americans are
now considered to be clinically overweight. These values mark significant increases over the
time period from 1988-1994 when the prevalence of obesity was 22.9% and the prevalence of
overweight was 55.9% (Flegal 2002). In the early 1960s, fewer than 1 in 4 Americans were
classified as overweight or obese (Manson 2003).
The fact that the prevalence of overweight and obesity is increasing in the United States
is an important health problem. Excess weight has been shown to be a major risk factor for
premature mortality, cardiovascular disease, type 2 diabetes mellitus, osteoarthritis, some types
of cancers, and many other medical conditions. Furthermore, almost 300,000 American adults
die annually from causes related to obesity. Overweight and obesity is not only a problem for
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the individual, though. The United States health care system currently spends about $51.7
billion on overweight and obesity. This accounts for 5.7% of the total United States health
expenditure. It is also estimated that overweight and obesity accounts for an additional $47.6
billion of indirect costs to society (http://www.niddk.nih.gov/health/nutrit/pubs/statobes.htm).
Together, this means that an almost $100 billion burden is placed on society because of
overweight and obesity.
It is therefore reasonable to examine ways to address this tremendous weight problem in
the United States. The increased prevalence of overweight and obesity is often accredited to
several factors: 1) increased consumption of food (“super-sizing” of meals), 2) greater
consumption of high-fat foods, 3) easily available high-calorie, good-tasting, low-cost foods, 4)
less active or more sedentary lifestyles (Blackburn 2001). While it has been well-shown that
living an active lifestyle, exercising, and monitoring eating habits are helpful in weight loss and
weight control, the merits of individual diets are still up for much debate. The rest of this paper
investigates the efficacy of a low-carbohydrate diet.
A low-carbohydrate diet may be considered based on several theoretical ideas. First, it
has been suggested that high-fat, high-protein, low-carbohydrate diets allow the dieter to feel
more satiated after a meal, thus causing the dieter to eat less. Furthermore, more of the foods
typical people like to eat will fall into this category making it easier for a dieter to follow his or
her plan. These are important considerations since they will most likely increase compliance
with the diet, therefore keeping off lost weight. Another theoretical consideration of a low-
carbohydrate diet is that such a diet would force the body to switch from carbohydrate
metabolism to fat-store metabolism, thus burning accumulated fat and reducing weight.
Similarly, such a diet could decrease insulin spikes after meals thus allowing the body to
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maintain a catabolic state. Finally, a low-carbohydrate diet would allow the dieter to maintain a
proper protein balance despite reduced caloric intake.
Several studies have shown that a diet low in carbohydrates leads to greater weight loss
than the standard, higher carbohydrate diet. The analysis of one low carbohydrate diet shows
that reducing carbohydrate content to less than 70g and restricting caloric intake without
changing protein or fat consumption promotes weight loss. Twenty overweight women
underwent 8 weeks of a low carbohydrate diet (50g/day) with energy restriction (reduced by
2644 kJ/day, from 8384 kJ to 5740 kJ) and lost an average of 5 kg and decreased their BMI by
1.8 kg/m2. In addition to weight loss, investigators measured BMI, percentage body fat, fasting
blood glucose, fasting serum insulin, oral glucose tolerance, free or total IGF, blood pressure,
and cholesterol levels. Improvements in body composition, blood pressure, and blood lipids
without compromising glucose tolerance in moderately overweight women were observed. The
effects of exercise on weight loss or other health factors were not studied. The authors of this
study claim that it demonstrates that a low carbohydrate diet is effective for losing weight and for
decreasing risk factors for cardiovascular disease; however, this conclusion is problematic for
several reasons. The low carbohydrate diet was also a low energy diet, so it is not clear if the
benefits are from reduced carbohydrates, or just from reducing the total energy intake of the
study participants. In addition, while the total cholesterol and LDL cholesterol had decreased by
the end of the 8 weeks, these levels were not significantly different from baseline values obtained
before the trial (Meckling 2002).
In an uncontrolled study by Westman et al. on the effects of a low-carbohydrate diet on
weight loss and cholesterol levels in men and women also showed weight loss, 66% of which
was estimated to be fat mass. Serum bicarbonate levels decreased in patients, but were within
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normal levels. Total cholesterol decreased by 11 mg/dL, LDL decreased by 10 mg/dl, and HDL
rose by 10 mg/dl. Non-HDL cholesterol decreased by 21, and triglycerides decreased 56 mg/dL
over a duration of 24 weeks. The diet composition was 23 +/- 10 g carbohydrates, 115 +/- 29 g
protein, 98+/-27 g fat, and caloric intake was unrestricted; however, mean daily caloric intake
was 1447 +/- 350 kcal. 51% of subjects complied with recommendations to exercise 3 or more
times per week on average during the study duration. While this study does demonstrate weight
loss with a low-carbohydrate diet, it is difficult to interpret its results in the absence of data from
a control group. It is possible that weight loss is due mostly to a decreased caloric intake
(despite the design of the study, which does not restrict caloric intake). Further, skin-fold
measurements were used rather than more precise techniques (Westman 2002).
The well known and popular Atkins’ diet was studied directly by Larosa et al. for 12
weeks. The researchers identified 24 obese (here, 10% above their maximum weight for height
by Metropolitan Life insurance tables) men and women and instructed them to follow the diet
described in Dr. Atkins’ Diet Revolution. The normal diet was followed for 2 weeks, and during
stage 1, study participants were instructed to consume no carbohydrates but were not given
caloric limits. After 4 weeks, stage 2 allowed 5-8 grams of carbohydrates in the diet for 4 more
weeks. After this time, the participants were instructed to resume their normal diet for the last 2
weeks of the study. LDL levels showed a significant increase, especially in women. Changes in
HDL were not significant. Free fatty acids and uric acid also showed a significant increase in
both men and women. Triglycerides were shown to fall significantly in men. The observed
weight loss for the combined groups was 7.7 +/- 0.73 kg; however half of the observed total
weight loss was during the first two weeks of the beginning of the study diet. These results may
be due to the elimination of carbohydrates that ordinarily cause water retention and
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unintentionally limiting calories while limiting carbohydrates. Therefore, this diet may be
effective for short term weight loss (Larosa 1980).
However, in another study with a longer duration of 6 months, overweight were put on
low carbohydrate (35% carbohydrate, 29.9% protein, 35.0% fat) or high carbohydrate (58%
carbohydrate, 20.7% protein, 20.5% fat) diets both with 1200 kcals/day hypocaloric intake. Less
effect on the difference in weight loss was observed between the two groups than in the
previously discussed studies, with the high carbohydrate group losing 4.2 pounds, and the low
carbohydrate group losing 5.4 pounds. The BMI of the low carbohydrate group was reduced by
2.2 kg/m2. The differences in all the other measured outcomes including LDL, HDL and
triglycerides were not significant. Adherence to each diet showed a 25% dropout rate for both
groups. Interestingly, postmenopausal women significantly lost more weight on low
carbohydrate diets than those on high carbohydrate diets. This study also did not consider the
effects of exercise on weight loss (Lean 1997).
The effects of a high-protein diet (≥25% energy intake) have been compared against
other options such as a “balanced” diet, a high-fat diet, or a high-carbohydrate diet. The major
health effects to be examined can be grouped into total weight loss, negative health effects, and
positive health effects. In order for one to contend that replacing one energy substrate with
another will grossly affect weight loss, one must believe that the new substrate is less energy
efficient or causes the organism’s behavior to change so that it uses or requires less energy. The
proponents of a high-protein diet believe that the thermic effect of feeding (TEF) should cause
the body to lose weight. Protein does contribute twice as much to TEF as carbohydrate, though
the studies that have examined this topic have found that in the best case scenario one might be
able to lose 0.09 kg/month as a result of this strategy. Even though this weight loss difference
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was theoretically possible, the studies examined by this group found that no significant weight
loss could be attributed to this substitution of energy substrate. As to behavior modification,
some studies (as reviewed by Eisenstein et al.) did indicate that there was an increase in satiety
from high-protein meals as compared to control meals, though no evidence was presented as to
the long-term stability of this effect. The biggest downfall of high protein diets appears to be
negative effects on the kidneys. Short-term studies indicate that increased protein intake is
associated with increased renal calcium excretion, negative calcium balance, and bone
resorption. In addition, one prospective study of >45,000 men age 40-75 showed that intake of
animal protein was directly associated with risk of symptomatic kidney stone formation
(Eisenstein 2002).
Other studies show that hypocaloric low carbohydrate diets do not result in any
differences in weight loss in comparison to hypocaloric high carbohydrate diets. In one 12 week
study that followed overweight men and women on low carbohydrate (25% carbohydrate, 30%
protein, 45% fat) and high carbohydrate (45% carbohydrate, 29% protein, 26% fat) hypocaloric
(<1200 kcal/day) diets showed choice of diet did not influence weight loss or adipose tissue loss
after 12 weeks. In addition to weight loss, BMI, LDL, HDL, triglycerides, and diet adherence
were measured. Compliance greater than 90% (judging by the weight loss compared to
predicted calorie deficit) was observed for both diets. The difference in the loss of lean body
mass was not statistically significant between the two groups, and similar improvements in
cholesterol, triglycerides, glucose, and glycemia were shown. However, basal insulin fell more
markedly in low carbohydrate diet, which may have been because of the higher monounsaturated
fat content in the low carbohydrate diet than in the high carbohydrate diet. The exercise level
was light to moderate for every patient. Shortcomings of this study are the relatively small
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sample size, small proportion of men, and lack of follow-up after 12 weeks. The authors also
replaced carbohydrates with fat in the low carbohydrate diet without looking at how varying
protein might affect results. Further, authors did not specify whether patients were randomized
to the two diets (Golay 1996).
Another hypocaloric diet study was conducted that randomized obese patients in this case
to low carbohydrate (15%) or high carbohydrate (45%) diet for 6 weeks with 2 hours of exercise
per day. The low carbohydrate diet had higher unsaturated fats compared to the high
carbohydrate diet, and protein content similar for each diet. There was no statistically significant
difference in percentage weight loss, percentage fat loss, or nitrogen loss between the low
carbohydrate and high carbohydrate diets after 6 weeks, and though the drop in fasting plasma
glucose, insulin, cholesterol, triglycerides, and HDL cholesterol was smaller in high
carbohydrate diet, the differences were not statistically significant. These several studies seem to
imply that weight loss is due to hypocaloric diet, not the relative composition of carbohydrates,
fats, and protein in the diets (Golay 2000).
Exercise has significant effects on the weight loss and other health factor results of low
carbohydrate diets. Since previous studies have shown that low-carbohydrate, high-fat diets lead
to an improvement in insulin sensitivity, the effects of a low-carbohydrate, high-fat diet on
insulin sensitivity and intracellular glucose processing in healthy, physically fit young men
without family histories of diabetes was studied over three weeks. The men were instructed to
continue their exercise regimens, and the group included 1 triathlete, 3 long-distance bicyclists, 4
runners, 2 runners/weight lifters. The low carbohydrate diet (8% carbohydrate, 17% protein, 75%
fat) was compared to the standard diet (51% carbohydrate, 14% protein, 35% fat), both with
normal caloric intake of approximately 3500 kcal/day. It was shown that the low carbohydrate
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diet caused a drop in mean fasting serum insulin levels from 36+/-6 to 12+/-2 pmol/L.
However, the mean fasting plasma glucose concentration was unchanged. Although the rate of
disappearance of glucose was not affected, substantial alterations in the routes of intracellular
glucose metabolism were seen. Glucose oxidation dropped under both basal conditions and
insulin infusion, while nonoxidative glucose metabolism increased. On the low carbohydrate
diet, insulin had a decreased ability to decrease net fat oxidation; however, free fatty acid levels
were promptly suppressed by insulin infusion on both diets. Myocyte PDH (pyruvate
dehydrogenase) activity decreased dramatically on low-carbohydrate diet. Insulin-stimulated
glycogen synthase activation was much greater during the low carbohydrate diet. These results
show that aerobic capacity is important in maintaining insulin-stimulated nonoxidative glucose
metabolism during a low carbohydrate diet. Further, in young, physically fit subjects, the
eucaloric substitution of fat for carbohydrates does not uniformly lead to a decrease in overall
insulin sensitivity. In normal individuals, physical conditioning and dietary composition interact
in modulating carbohydrate metabolism (Cutler 1995).
In another study, 23 obese women were randomly assigned to aerobic exercise or no
exercise and to energy restricted low fat (60% carbohydrate, 25% protein, 15% fat )or low
carbohydrate 25% carbohydrate, 25% protein, 50% fat) diets both with reduced caloric intake
(1200kcal/day for non-exercising group) for 12 weeks. Prescribed intakes for subjects assigned
to the exercise groups were increased to compensate for the calculated energy costs of the
exercise sessions. Exercise was found to increase loss of fat tissue as opposed to fat-free tissue
(muscle, bone, etc.). Aerobic exercise significantly enhanced fat loss by 2.7 kg. Slightly higher
weight loss was observed with low carbohydrate compared to low fat diet (10.6 kg vs. 8.1 kg)
but no difference in body composition was seen. It can be suggested that the decrease in the rate
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of weight loss with time found in low-energy diets is because of losses of fat-free body mass,
which could cause reductions in resting metabolism, decreases in postprandial energy
expenditure because of smaller meals, and decreases in the energy cost of movement because of
smaller body size (Racette 1995).
Some studies have shown that the difficulty of complying with the low carbohydrate diet
may reduce the theoretical effectiveness of the diets in practice. Landers et al. describes a study
done on 91 obese patients between the ages of 18 and 55. Each patient was randomly assigned
to one of three dieting groups: low carbohydrate, high protein diet (less than 30g carbohydrate
per day); The Zone Diet (snack of 40 % carbohydrate, 30% protein, 30% fat five times a day); a
conventional diet (reduced calories, 50% carbohydrate, 20% protein, 30% fat). These diets allow
the energy needed to promote weight loss of .45 kg/week. The observed mean weight loss after
12 weeks of dieting was 5.2 kg. There were no significant differences between the different
dieting groups. It is difficult to analyze the results of the study due to the high patient drop out
(49 out of 91 original subjects completed the study), and due to poor diet compliance among the
participants. Following completion of the study, no dieters from the low carbohydrate or high
protein group continued with their diets. Zone dieters generally liked their diet. Conventional
plan dieters felt the experimental diet closely approximated a well-balanced eating plan that
would promote healthy eating habits. In light of these results, the researches recommend that
weight loss instructions be kept simple for patients (Landers 2002).
While a number of studies have attempted to study the effects of a low-carbohydrate diet
on weight loss and other parameters of health, there are many difficulties in drawing definitive
conclusions from these studies. The duration of most studies ranged from several weeks to up to
six months, with little or no long term follow up. Thus, we are left with little information on
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long-term diet adherence, weight loss, cardiovascular health, insulin tolerance, etc. All the
same, some conclusions can be drawn by examining several parameters in combination – body
weight lost, metabolic parameters, body composition, nutritional adequacy, and compliance.
It seems that a hypocaloric diet, regardless of its nutritional breakdown, will result in
weight loss, since it is really the reduction of calories consumed that drives weight loss. The
obvious plan for weight loss, then, would be simply to eat less. The difficulty is in convincing
Americans to eat less and to continue to eat less on a permanent basis.
Numerous studies have shown that high-fat and high-carbohydrate diets can cause
cardiovascular disease and diabetes, respectively, as well as a variety of other health problems.
In low carbohydrate diets, the calories tend to be replaced by proteins, which as discussed above,
can lead to negative effects on the kidneys. Nevertheless, it seems that all forms of weight loss,
regardless of the approach taken, lower blood lipid levels, improve glycemic control, and lower
blood pressure (Freedman 2001).
When losing weight, body composition is important to consider because ideally, one
would lose body fat, rather than lean body mass or some other component. High-fat, low-
carbohydrate ketogenic diets cause a greater loss of body water than body fat at first, resulting in
the regaining of water weight when the diet ends. In the long run, though, all diets result in the
loss of body fat.
Another important factor to look at in choosing a diet is whether or not the restrictions
allow for balanced, nutritionally-adequate meals. High-fat, low-carbohydrate diets are low in
vitamins E, A, thiamin, B6, folate, calcium, magnesium, iron, potassium, and dietary fiber, and
thus require supplementation. Very low fat diets are also nutritionally inadequate, since they are
low in vitamins E, B12, and zinc.
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Finally, the issue of compliance is perhaps the most important, since no diet will be
effective unless people are willing to follow it. As brought up in the study by Landers et al, a
diet with simple guidelines seems to be the easiest for patients to follow. In this respect, a
conventional diet with balanced food groups might be the easiest to maintain. Another major
complaint is that diets which cut calories leave one feeling hungry all the time. Diets high in
protein and fat appear to lead to greater satiety, which could lead to better compliance.
Obviously, there is no simple answer as to which diet is the best. Each diet has
advantages and disadvantages, as well as components that have not yet been adequately research
to draw definitive conclusions about. Perhaps the best recommendation, then, is for patients to
choose their diet on a case by case basis. A patient who complains of feeling hungry all the time
on conventional foods may benefit from a high-protein diet such as the Atkins diet; a patient with
little time to prepare special foods, however, may be best off with a balanced, low-fat diet.
Patients with kidney disease or osteoporosis may want to avoid high protein diets, and patients
with cardiovascular disease may want to avoid substituting fats for carbohydrates. Of course,
there may be other positive and or negative health effects to distinguish the various diets that are
not yet apparent. Finally, there are behavioral factors that are important for all diets regardless of
the nutritional breakdown, such as exercise and behavioral modifications, including self-
weighing. In the end, all diets seem to boil down to calorie restriction, so personal factors may
outweigh any other advantages or disadvantages in maintaining a successful diet.
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References http://www.niddk.nih.gov/health/nutrit/pubs/statobes.htm Blackburn GL, Phillips JC, Morreale S. Physician's guide to popular low-carbohydrate weight-loss diets. Cleveland Clinic Journal of Medicine. Sep 2001; 68(9):761, 765-6, 768-9, 773-4. Bravata DM, Sanders L, Huang J, Krumholz HM, Olkin I, Garnder CD, Bravata DM. Efficacy and Safety of Low-Carbohydrate Diets: A Systematic Review. JAMA. 2003; 289(14):1837-1850. Bray GA. Low-Carbohydrate Diets and Realities of Weight Loss. JAMA. 2003; 289(14):1853-5. Cutler DL, Gray CG, Park SW, Hickman MG, Bell JM, and Kolterman OG. Low Carbohydrate Diet Alters Intracellular Glucose Metabolism But Not Overall Glucose Disposal in Exercise-Trained Subjects. Metabolism. Oct 1995; 44(10):1264-1270. Eisenstein J, Roberts SB, Dallal G, & Saltzman E. High-protein Weight-loss Diets: Are They Safe and Do They Work? A Review of the experimental and epidemiologic data. Nutrition Reviews. July 2002; 60(7):189-200. Flegal KM, Carroll MD, Ogden CL, Johnson CL. Prevalence and Trends in Obesity Among US Adults, 1999-2000. JAMA. 2002;288:1723-7. Freedman MR, King J, Kennedy E. Popular Diets: A Scientific Review. Obesity Research. March 2001; 9(Suppl1):1S-39S. Golay A, Eigenheer C, Morel Y, Kujawski P, Lehmann T, de Tonnac N. Weight-loss with low or high carbohydrate diet? International Journal of Obesity & Related Metabolic Disorders: Journal of the International Association for the Study of Obesity. Dec 1996; 20(12):1067-72. Golay A, Allaz AF, Ybarra J, Bianchi P, Saraiva S, Mensi N, Gomis R, de Tonnac N. Similar weight loss with low-energy food combining or balanced diets. International Journal of Obesity & Related Metabolic Disorders: Journal of the International Association for the Study of Obesity. Apr 2002; 24(4):492-6. Hensrud DD. Dietary treatment and long-term weight loss and maintenance in type 2 diabetes. Obesity Research. Nov 2001; 9 Suppl 4:348S-353S. Johnson RK. Frary C. Choose beverages and foods to moderate your intake of sugars: the 2000 dietary guidelines for Americans--what's all the fuss about? Journal of Nutrition. Oct 2001; 31(10):2766S-2771S.
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Klein S, Wadden T, Sugerman HJ. AGA Technical Review on Obesity. Gastroenterology 2002;123:882-932. Landers P, Wolfe MM, Glore S, Guild R, Phillips L. Effect of weight loss plans on body composition and diet duration. Journal - Oklahoma State Medical Association. May 2002; 95(5):329-31. Larosa JC, Fry AG, Muesing R, Rosing DR. Effects of high-protein, low-carbohydrate dieting on plasma lipoproteins and body weight. J Am Diet Assoc Sep 1980;77(3):264-70 Layman DK, Boileau RA, Erickson DJ, Painter JE, Shiue H, Sather C, Christou DD. A Reduced Ratio of Dietary Carbohydrate to Protein Improves Body Composition and Blood Lipid Profiles during Weight Loss in Adult Women. Journal of Nutrition. 2003; 133:411-417. Lean ME, Han TS, Prvan T, Richmond PR, Avenell A. Weight loss with high and low carbohydrate 1200 kcal diets in free living women. European Journal of Clinical Nutrition. Apr 1997; 51(4):243-8. Manson JE, Bassuk SS. Obesity in the United States: A Fresh Look at Its High Toll. JAMA. 2003;289:229-30. McGuire MT, Wing RR, Klem ML, Hill JO. Behavioral Strategies of Individuals Who Have Maintained Long-Term Weight Losses. Obesity Research. July 1999; 7(4):334-341. Meckling KA, Gauthier M, Grubb R, Sanford J. Effects of a hypocaloric, low-carbohydrate diet on weight loss, blood lipids, blood pressure, glucose tolerance, and body composition in free-living overweight women. Can J Physiol Pharmacol Nov 2002;80(11):1095-105. Parker B, Noakes M, Luscombe N, Clifton P. Effect of a high-protein, high-monounsaturated fat weight loss diet on glycemic control and lipid levels in type 2 diabetes. Diabetes Care. 2002; 25(3):425-30. Racette SB, Schoeller DA, Kushner RF, Neil KM, Herling-Iaffaldano K. Effects of aerobic exercise and dietary carbohydrate on energy expenditure and body composition during weight reduction in obese women. American Journal of Clinical Nutrition. Mar 1995; 61(3):486-94. Skov AR, Toubro S, Ronn B, Holm L, Astrup A. Randomized trial on protein versus carbohydrate in ad libitum fat reduced diet for the treatment of obesity. International Journal of Obesity & Related Metabolic Disorders: Journal of the International Association for the Study of Obesity. May 1999; 23(5):528-36. St Jeor ST. Howard BV. Prewitt TE. Bovee V. Bazzarre T. Eckel RH. Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association.
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Dietary protein and weight reduction: a statement for healthcare professionals from the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association. Circulation. 104(15):1869-74, Oct 9 2001. Ullrich IH, Peters PJ, Albrink MJ. Effect of Low-Carbohydrate Diets High in Either Fat or Protein on Thyroid Function, Plasma Insulin, Glucose, and Triglycerides in Healthy Young Adults. Journal of the American College of Nutrition. 1985; 4:451-459. Westman EC, Yancy WS, Edman JS, Tomlin KF, Perkins CE. Effect of a 6-month adherence to a very low carbohydrate diet program. American Journal of Medicine. 2002;113(1):30-36.
The Effects of a Low Carbohydrate Diet The Effects of a Low Carbohydrate Diet on Health Risk Factors, Weight Loss and on Health Risk Factors, Weight Loss and
ComplianceCompliance
Health Promotion and Disease Health Promotion and Disease Prevention Symposium Prevention Symposium
May 6, 2003May 6, 2003
Defining Obesity Defining Obesity
BMI is kg/mBMI is kg/m22
Normal is between 18 and 24.Normal is between 18 and 24.Overweight is 25 kg/mOverweight is 25 kg/m22 or greater.or greater.Obese is 30 kg/mObese is 30 kg/m22 or greater.or greater.
Major increase in obesity over the past 40 Major increase in obesity over the past 40 years years
1960’s <25% obese or overweight1960’s <25% obese or overweight2000 64.5% are obese or overweight2000 64.5% are obese or overweight
Why do we care? Why do we care?
CoCo--morbiditymorbidityCostCostClinical ObstaclesClinical Obstacles
Dieting Dieting
Fad dietsFad dietsWeight loss programsWeight loss programs“Clinically proven” popular diets“Clinically proven” popular diets
Atkins DietAtkins DietZone DietZone Diet
Investigating ObesityInvestigating ObesityBMIBMIBody Fat %Body Fat %Fasting blood glucoseFasting blood glucoseSerum insulinSerum insulinOral glucose toleranceOral glucose toleranceFree and total IGFFree and total IGFBPBPCholesterol (lipid profile: HDL/LDL)Cholesterol (lipid profile: HDL/LDL)ComplianceCompliance
Study DesignStudy Design
DurationDurationPatient PopulationPatient PopulationFollowFollow--upup
ExerciseExerciseControlControlTotal CaloriesTotal Calories
ComplianceCompliance
Restricted diet Restricted diet DropDrop--outsoutsExercise regimensExercise regimensInpatient vs. Outpatient studiesInpatient vs. Outpatient studies
Problems with StudiesProblems with Studies
Controlled vs. UnControlled vs. Un--controlled controlled Comparison Comparison Compliance and enrollmentCompliance and enrollmentMethods and measurementsMethods and measurementsSample sizeSample sizeDuration of studyDuration of study
So, what about Atkins?So, what about Atkins?
Study Design:Study Design:Weeks 1Weeks 1--2: normal diet2: normal dietWeeks 3Weeks 3--6: no 6: no CHOsCHOs, no caloric limit in , no caloric limit in other categoriesother categoriesWeeks 7Weeks 7--9: limit 59: limit 5--8 grams of 8 grams of CHOsCHOsper day, no limits in other categoriesper day, no limits in other categoriesWeeks 10Weeks 10--12: resume normal diet12: resume normal diet
Results Results
LDL levels increased significantly, HDL LDL levels increased significantly, HDL levels did not change significantlylevels did not change significantlyFFAsFFAs increased significantlyincreased significantlyTriglycerides fell significantly in menTriglycerides fell significantly in menObserved weight loss: 16.94 +/Observed weight loss: 16.94 +/-- 1.61 1.61 lbs, approximately half of this weight lbs, approximately half of this weight loss occurred during the initial 2 weeksloss occurred during the initial 2 weeks
Problems with studyProblems with study
Small sample sizeSmall sample sizeIncomplete measurement of endpointsIncomplete measurement of endpointsWeight loss attributed to?Weight loss attributed to?Short followShort follow--upupComplianceCompliance
Authors’ favorite diet:Authors’ favorite diet:Random AssignmentRandom AssignmentCompare 3 groups:Compare 3 groups:
Low calorie (unrestricted content)Low calorie (unrestricted content)low low carbcarb/ high protein and fat/ high protein and fatlow fat/ high low fat/ high carbcarb and proteinand protein
Large sample sizeLarge sample sizeJournalJournalMonitor compliance Monitor compliance
plasma glucose plasma glucose urine nitrogenurine nitrogen
Conclusion Conclusion
Weight loss: caloric output > caloric intake Weight loss: caloric output > caloric intake No agreement on “the best” dietNo agreement on “the best” diet
Low Low carbcarb diets diets satiation with low calorie satiation with low calorie intake (intake (Eisenstein et al, 2002)Eisenstein et al, 2002)
Diet must be tailored to each patientDiet must be tailored to each patient