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| Low Carbohydrate Diets for Weight Loss: Myth or Reality? By Theresa Glanville Ph.D, PDt, Low carbohydrate (CHO), high protein diets, promising quick weight loss without hunger or self-deprivation, are the rage. This approach to weight loss is not new and regularly resurfaces in the popular press, each time with a new twist, supported by testimonials and anecdotal reports rather than scientific evidence. The underlying premise of the diets is that consumption of CHO-rich foods stimulates over-production of insulin, the hormone responsible for the transport and storage of glucose and, under certain conditions, fat. Since protein-rich foods are reported to have less impact on insulin secretion, by substituting protein-rich foods for CHO-rich foods in these diets, it is proposed that stored fat is used for energy.
Body fatness reflects the balance between energy intake and expenditure. Proponents of CHO-restricted diets claim that weight loss can occur without a reduction in total energy intake. However, analysis of several CHO-restricted diets reveals that they are energy-reduced, often containing 800 - 1200 kcal per day, similar to conventional reducing diets. This is because the types of food and combinations allowed are very prescriptive. For example, one diet claims you can eat all the steak, bacon and eggs you want, but severely restricts consumption of grains, dairy, fruits and vegetables, thereby limiting total food consumption. Research comparing an energy-reduced (1200 kcal/day) CHO-restricted diet (75g/ day) with a conventional carbohydrate-rich diet (225 g/day) that similarly restricts energy intake, showed that both approaches produce weight loss, but that overall decrease in the early phase of dieting was greater with CHO restriction(1). This was largely due to sodium excretion and water loss associated with utilization of stored glycogen. Both of these components of weight loss will be rapidly regained when normal food intake is resumed, and glycogen stores are replenished. Regardless of whether the energy restricted diet is CHO-restricted or CHO-rich, the loss of body fat, as a component of the loss of body weight, is the same(2,3). Significant and sustained weight loss is a difficult goal. The reward of rapid weight loss during early CHO-restriction may increase compliance. Likewise, extreme CHO restriction can produce ketosis marked by loss of appetite – which can be an additional compliance factor. Over the long term, this type of diet is monotonous and difficult to maintain. Health concerns include possible deficiencies in calcium, potassium, and the B vitamins. The impact of excess nitrogen intake may also worsen pre-existing conditions such as gout, liver and kidney disease. References
Carbohydrate Intake and Obesity – An Epidemiological Perspective By Alison Stephen Ph.D CANTOX Health Sciences International, ON In an era of enthusiasm for low carbohydrate diets as the answer for weight control, it is worthwhile to note that most observational studies do not support such a conclusion. Large dietary surveys conducted on different age groups in numerous countries show inverse relationships between obesity and carbohydrate intake, both in grams per day and as percentage of energy, in contrast to positive relationships with dietary fat(1,2). Research with adult American males, using skin fold to assess body fat, found the fattest subjects ate more fat and less carbohydrate than lean subjects(3). Similarly, a recent survey in Spain showed lower carbohydrate intakes were found in overweight adolescents compared to those of normal weight(4). The same trends are seen in children. Recent surveys of U.K. school children and preschool children showed inverse relationships between carbohydrate intake and BMI(5). Perhaps the greatest surprise in these surveys was that high intakes of sugars were associated with diets of lower energy density, unlike high fat diets, which are energy dense. Energy density is now considered to be a prime determinant of overconsumption of foods. Also, a number of well controlled studies indicate that the total weight of food is critical for weight control(6). Removal of sugars from the diet actually leads to increased energy density, hence weight gain, because the sugars tend to be replaced weight for weight, in part, by the more calorically dense nutrient, fat. Maintenance of a healthy weight requires long term dietary management. Evidence from habitual diets of populations suggests that high carbohydrate diets, with low energy density, are the way to go to improve Canadians’ risk for and management of overweight and obesity. References
Research Update Abstract Objective To examine the association between a range of health and nutrition indicators and popular diets.
Design The Continuing Survey of Food Intake by Individuals (CSFII) 1994-1996 were used to examine the relationship between prototype popular diets and diet quality as measured by the healthy eating index (HEI), consumption patterns, and body mass index (BMI). The prototype diets included vegetarian (no meat, poultry, or fish on day of survey) and non-vegetarian. The non-vegetarian group was further subdivided into low carbohydrate (less than 30% of energy from carbohydrate), medium (30% to 55%), and high (greater than 55% of energy). Within the high carbohydrate group, participants were classified as having Pyramid or non-Pyramid eating patterns. The Pyramid group was defined as 30% or less of energy from fat and at least one serving from the five major food groups in the USDA Food Guide Pyramid. Finally, the non-Pyramid group was further subdivided into low fat (less than 15% of energy from fat) and moderate fat (15% to 30% of energy from fat). In addition, a review of the published scientific literature was conducted; all studies identified were included in the review. Subjects 10,014 adults, aged 19 years and older, from the 1994-1996 CSFII were included in the analyses of extant data. More than 200 individual studies were included in the review of the literature. Results Analyses of the CSFII indicate that the diet quality as measured by HEI was highest for the high carbohydrate Pyramid group (82.9) and lowest for the low carbohydrate group (44.6). Energy intakes were low for the vegetarians (1,606 kcals) and high carbohydrate/low fat group (1360 kcals). BMIs were lowest for women in the vegetarian group (24.6) and the high carbohydrate/low fat group (24.4); for men, the lowest BMIs were observed for vegetarians (25.2) and the high carbohydrate Pyramid group (25.2). Review of the literature suggests that weight loss is independent of diet composition. Energy restriction is the key variable associated with weight reduction in the short term. Conclusions: Diets that are high in carbohydrate and low to moderate in fat tend to be lower in energy. The lowest energy intakes were observed for those on a vegetarian diet. The diet quality as measured by HEI was highest for the high carbohydrate groups and lowest for the low carbohydrate groups. The BMIs were significantly lower for men and women on the high carbohydrate diet; the highest BMIs were noted for those on a low carbohydrate diet. Reprints of the complete article may be obtained from the Canadian Sugar Institute by email at info@sugar.ca
Consumer awareness, trial and attitudes towards low carbohydrate diets were investigated by Ipsos-ASI as part of the national Sugar Tracking Study 2000, conducted on behalf of the Canadian Sugar Institute. A representative sample of adult consumers were interviewed in English in major cities in Ontario and Western Canada and in French in Quebec. Highlights of the study findings follow. General awareness of diets Less than half (46%) of consumers indicated that they were aware of any weight-loss diets that are based on the principle of reducing carbohydrate intake. Awareness of these diets was stronger in English Canada (50%) than in French Quebec (37%), and was stronger in respondents older than 35, in women, and among those with higher incomes. Awareness of specific diets When prompted with a list of 8 specific low carbohydrate diets, awareness was dramatically higher (82%) amongst the general population. A surprising 96% of French Quebec respondents indicated awareness of at least one of the diets versus 76% in English Canada. The substantially higher levels of reported awareness of the specific diets versus the lower levels of general awareness suggests that consumers do not fully understand the fundamental basis of the diets – that they are designed on the principle of reducing carbohydrate intake. Most popular diets Among the specific diets, consumer awareness of “Eat Yourself Slim” by Michel Montignac stands out for having achieved almost ubiquitous awareness in the French Quebec market. At 92% reported awareness, it is the clear leader amongst carbohydrate-reduced diets in French Quebec. Within English Canada, “Dr. Atkins’ New Diet Revolution” (45%), “Protein Power” (39%) and Suzanne Somers’ “Get Skinny on Fabulous Foods” (35%) received the greatest awareness. Users of diets Despite the high levels of awareness of the low carbohydrate diets, limited experience with these diets was reported. In French Quebec, the “Montignac Diet” achieved a trial rate of 13% - essentially the only low carbohydrate experience for dieters in this region. In English Canada, trial rates were low across all of the specific diets, with 7% having tried any of the diets. The “Carbohydrate Addicts Diet”, with a 3% trial rate, was the most popular in this region. Attitudes about diets among users While there was limited trial of the specific diets recorded, they achieved a level of validity amongst their users. Dieters had high agreement ratings on a variety of concepts, including effectiveness for losing weight, fit with healthy eating, and that they can be followed for long periods of time. Characteristics of users of diets Those who have tried the low carbohydrate diets tended to be women, were within the age range of 35-44 years, and generally had higher levels of education and annual household incomes. These consumers indicated a greater likelihood to watch what they eat because they are concerned about their weight, rather than about their general health. These findings indicate that although most consumers are aware of popular low carbohydrate diets by name, they generally do not recognize them as low carbohydrate diets. It is likely that the popularity and media attention around these diets have served to impact consumers’ perceptions of healthy eating and the role of carbohydrates in a balanced diet and lifestyle.
Carbohydrate Lit Scan McDevitt RM, Poppitt SD, Murgatroyd PR, Prentice AM., Macronutrient disposal during controlled overfeeding with glucose, fructose, sucrose or fat in lean and obese women., Am J Clin Nutr, 2000;72:369-377. This study assessed energy expenditure and glycogen or fat storage in lean and obese women who consumed a measured excess of dietary energy, in the form of various sugars or fat. The study confirmed that carbohydrates take precedence over fat for fuel selection, that glycogen stores are regulated within a narrow range, and that fat is used as an energy reservoir. The authors concluded that carbohydrates do not disproportionately stimulate fat storage and that dietary fat is more likely to lead to fat deposition. Saris WHM et al., Randomized controlled trial of change in dietary carbohydrate/fat ratio and simple vs complex carbohydrates on body weight and blood lipids: the CARMEN study., Int J Obes, 2000;24:1310-1318. The Carbohydrate Ratio Management in European National (CARMEN) diets trial studied the effects of reducing the intake of fat and increasing intake of sugars or starches on body weight and blood lipids, over an extended period of time, in a community-based population. All high carbohydrate diets studied produced a modest yet significant reduction in body weight and fatness, with no adverse impact on blood lipids. Wolever TMS., Dietary carbohydrates and insulin action in humans., Br J Nutr, 2000;83(Suppl 1):S97-S102. This review examines the role of dietary carbohydrate in the treatment of the metabolic syndrome. Reducing postprandial glucose and insulin responses may interrupt the progression of the metabolic syndrome, but nutrition researchers do not yet agree on the best way to achieve this effect. Reducing dietary carbohydrate may actually increase carbohydrate intolerance, and the impact of low glycemic index carbohydrate food choices has not been adequately studied. More research is needed to identify the optimal amount and type of carbohydrate for treatment of the metabolic syndrome Sievenpiper JL et al., Simple skinfold measurements complement conventional anthropometric assessments in predicting glucose tolerance., Am J Clin Nutr 2001;73:567-574. A cross-section of 35 subjects was studied to assess whether skinfold thickness measurements complement conventional measurements of body mass index (BMI), total body fat, waist-to-hip ratio, and waist circumference in predicting glucose and insulin regulation. Skinfold measurements were found to be strongly correlated with various indices of glucose and insulin regulation and when added to other anthropometric measurements explained more of the differences in glucose and insulin regulation than these measurements did alone. It was concluded that concurrent use of skinfold measurements with other simple anthropometric office measurements might give a more complete picture of risk for abnormal glucose and insulin regulation Carbohydrate News Carbohydrate News is an annual publication of the Canadian Sugar Institute (CSI). CSI maintains a scientific library and comprehensive computer database of current literature, government documents and technical information pertaining to carbohydrate, sugars and alternative sweeteners. CSI also publishes resource material for health professionals, educators and the public. CSI gratefully acknowledges the contributions made by the Editorial Board as well as Susan Fyshe, M.H.Sc., RD, for her role in editing this newsletter. For more information, contact: Canadian Sugar Institute, Nutrition Information Service 10 Bay Street, Suite 620, Toronto, ON, M5J 2R8 Fax: (416) 368-6426, www.sugar.ca Editorial Board Harvey Anderson, Ph.D. Marianne Lamb, RN, M.N. Rena Mendelson, D.Sc., RD Anthony M. Ocana, M.Sc., RDN, MD, CCFP Alison M. Stephen, Ph.D. Huguette Turgeon O’Brien, Ph.D., Dt.P. This publication may be reproduced provided the source is acknowledged. |
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Canadian Sugar Institute
10 Bay Street, Suite 620 - Toronto, Ontario, M5J 2R8
Tel: 416-368-8091 - Fax: 416-368-6426 | info@sugar.ca
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