The role of dietary fat in body fatness: evidence from a preliminary meta-analysis of ad libitum low-fat dietary intervention studies

The role of high-fat diets in weight gain and obesity has been questioned because of inconsistent reports in the literature concerning the efficacy of ad libitum low-fat diets to reduce body weight. We conducted a meta-analysis of weight loss occurring on ad libitum low-fat diets in intervention trials, and analysed the relationship between initial body weight and weight loss. We selected controlled trials lasting more than 2 months comparing ad libitum low-fat diets with a control group consuming their habitual diet or a medium-fat diet ad libitum published from 1966 to 1998. Data were included from 16 trials with a duration of 2-12 months, involving 1728 individuals. No trials on obese subjects fulfilled the inclusion criteria. The weighted difference in weight loss between intervention and control groups was 2.55 kg (95% CI, 1.5-3.5; P < 0.0001). Weight loss was positively and independently related to pre-treatment body weight (r = 0.52, P < 0.05) and to reduction in the percentage of energy as fat (0.37 kg/%, P < 0.005) in unweighted analysis. Extrapolated to a BMI of about 30 kg/m2 and assuming a 10% reduction in dietary fat, the predicted weight loss would be 4.4 kg (95% CI, 2.0 to -6.8 kg). Because weight loss was not the primary aim in 12 of the 16 studies, it is unlikely that voluntary energy restriction contributed to the weight loss. Although there is no evidence that a high intake of simple sugars contributes to passive overconsumption, carbohydrate foods with a low glycaemic index may be more satiating and exert more beneficial effects on insulin resistance and cardiovascular risk factors. Moreover, an increase in protein content up to 25% of total energy may also contribute to reducing total energy intake. In conclusion, a low-fat diet, high in protein and fibre-rich carbohydrates, mainly from different vegetables, fruits and whole grains, is highly satiating for fewer calories than fatty foods. This diet composition provides good sources of vitamins, minerals, trace elements and fibre, and may have the most beneficial effect on blood lipids and blood-pressure levels. A reduction in dietary fat without restriction of total energy intake prevents weight gain in subjects of normal weight and produces a weight loss in overweight subjects, which is highly relevant for public health.     

Dietary management of obesity

BACKGROUND: The optimal diet for prevention of weight gain, obesity, metabolic syndrome, and type 2 diabetes is fat-reduced, fiber-rich, high in low-energy density carbohydrates (fruit, vegetables, and whole grain products), and intake of energy-containing drinks is restricted. RESULTS ON DIETARY FAT: The reduction of the total fat content of ad libitum diets produces weight loss in both the short term and over periods as long as 7 years. A fat-reduced diet, combined with physical activity, reduces almost all risk factors for cardiovascular disease and reduces the incidence of type 2 diabetes. The combination of reduction of dietary fat and energy, and increased physical activity has been shown to reduce the incidence of diabetes by 58% in 2 major trials. In post hoc analyses, the reduction in dietary fat (energy density) and increase in fiber were the strongest predictors of weight loss and diabetes-protective effects. LOW-GLYCEMIC INDEX AND HIGH-PROTEIN DIETS: It remains to be shown whether a low-glycemic index diet provides any benefit to weight control beyond this. Low-carbohydrate diets may be an option for inducing weight loss in obese patients, but a very low intake of carbohydrate-rich foods is not commensurate with a healthy and palatable diet in the long term. However, there is evidence that increasing the protein content of the diet from 15% up to 20%-30%, at the expense of carbohydrates, increases the satiating effect of the diet, and induces a spontaneous weight loss, and this could turn out to be a preferred option for patients with metabolic syndrome and type 2 diabetes.     

Dietary fibres in the regulation of appetite and food intake. Importance of viscosity

Dietary fibres have many functions in the diet, one of which may be to promote control of energy intake and reduce the risk of developing obesity. This is linked to the unique physico-chemical properties of dietary fibres which aid early signalling of satiation and prolonged or enhanced sensation of satiety. Particularly the ability of some dietary fibres to increase viscosity of intestinal contents offers numerous opportunities to affect appetite regulation. Few papers on the satiating effect of dietary fibres include information on the physico-chemical characteristics of the dietary fibres being tested, including molecular weight and viscosity. For viscosity to serve as a proxy for soluble dietary fibres it is essential to have an understanding of individual dietary fibre viscosity characteristics. The goal of this paper is to provide a brief overview on the role of dietary fibres in appetite regulation highlighting the importance of viscosity.     

Obesity: an inherited metabolic deficiency in the control of macronutrient balance?

It has generally been assumed that the body is 'energy blind' and calories from all three macronutrients contribute with the same value to energy balance. There is, however, accumulating evidence to suggest that during ad-libitum conditions energy balance is achieved by a separate regulation of carbohydrate, fat and protein balances. Regulation of carbohydrate balance has the highest priority in the hierarchy, which is appropriate because the limited glycogen stores are only capable of covering the carbohydrate oxidation for a few days. Due to the higher satiating power of carbohydrate and protein compared with fat, a reduction in the dietary fat/carbohydrate ratio produces a negative fat balance in normal subjects consuming the diet ad libitum, while an increase in dietary fat/carbohydrate ratio results in a positive fat balance and weight gain. Subjects with a genetically determined predisposition to obesity become obese when they are exposed to a particular range of environmental conditions. The available knowledge suggests that the genetic propensity to weight gain is caused by a susceptibility to dietary fat due to an impaired capacity to increase their lipid/carbohydrate oxidation when fed a high-fat/low-carbohydrate diet. This in turn promotes lipid storage, depletion of carbohydrate stores and increases appetite. By enlarging the fat stores, the accompanying insulin resistance and higher levels of circulating non-esterified fatty acids increase lipid oxidation until it is commensurate with the dietary fat intake. The development of obesity may therefore be viewed as a regulatory mechanism by which the impaired lipid oxidation rate is raised to match a high fat intake. However, by decreasing the dietary ratio of fat to carbohydrate, macronutrient balance may be achieved with a high energy expenditure and a normal body composition. The results support current dietary recommendations, but with less emphasis on carbohydrate source, and they are also applicable for the prevention and treatment of obesity.     

Dietary fibre and satiety

Summary  Dietary fibres have different physiological effects and provide a variety of health benefits, including satiety. They are thought to impact on satiation (the satisfaction of appetite during feeding that marks the end of eating and satiety (inhibition of hunger as a result of having eaten), because of their properties of adding bulk (satiation) and producing viscosity (satiety). Pre-absorptive factors, such as gastric distention, and the work and time required for chewing are important for satiation. For this reason, the bulking and textural properties of fibre make it an attractive ingredient for enhancing satiation. Adding bulk to the diet with fibre will also reduce the energy density of the diet. Satiety signals are generated both pre- and post-absorptively. Viscous soluble fibres may be useful because they prolong the intestinal phase of nutrient digestion and absorption. This means that there is a longer time over which the macronutrients can interact with the pre-absorptive mechanisms of satiation and satiety, as well as prolong the time course of post-absorptive signals. Diets low in energy and fat, such as those typically recommended for obese people, are poorly satiating. Adding fibre to low-calorie/low-fat foods may enhance satiety, but because weight-loss meals are low in energy and fat, satiety is likely to be short lasting. Not all dietary fibre has an impact on satiety. We review types of dietary fibre, whole foods that contain dietary fibre, and published studies on the effect of these fibres on satiety.     

A clinical trial to selectively change dietary fat and/or energy intake in women: the Women's Diet Study.

Dietary fat and energy intake have been implicated in breast cancer etiology. To examine the relative importance of these dietary factors on markers of cancer risk in women, we designed an intervention trial to selectively decrease fat and/or energy intake in free-living, premenopausal women who were somewhat overweight. The study used a 2 x 2 factorial design to evaluate the independent and interactive effects of dietary fat and energy. The diets were nonintervention, low fat (15% of energy from fat, maintenance of energy intake), low energy (25% energy reduction), and combination low fat and low energy. We utilized an individualized counseling approach with self-selection of foods. Women on the low-fat and combination diets were asked to meet given daily goals for fat grams and food group exchanges, while women on the low-energy diet used only food group exchanges. Of the 113 premenopausal women randomized who were eligible for analysis, 43% were African-American. A total of 88 women completed the 12-week program, and adherence to the dietary goals was similar in both racial groups. Women on the low-fat diet were able to reduce dietary fat intake to 19% of energy by 4 weeks and to 17% by 12 weeks with a slight decrease in energy intake. Women on the low-energy diet met their energy reduction goals by four weeks while maintaining percentage of energy from fat. Women on the combination diet largely met their goals by four weeks as well. These data indicate that it is possible to selectively manipulate dietary fat and energy intake in women over a short period of time, which makes clinical studies on the relative effects of these two dietary variables on cancer risk biomarkers readily feasible.     

Relationship between eating behaviours and food and drink consumption in healthy postmenopausal women in a real-life context

Associations between eating behaviours and dietary variables have not been thoroughly investigated in healthy postmenopausal women in a real life uncontrolled context. To investigate how eating behaviours (cognitive dietary restraint, disinhibition and susceptibility to hunger) were associated with food and drink consumption, energy density and meal pattern in 112 healthy postmenopausal women (age 56.8 (SD 4.4) years) not on.hormonal therapy. Women completed a 3 d weighed food record and filled out the Three-Factor Eating Questionnaire. The sample was divided according to the median of the distribution of cognitive dietary restraint and disinhibition (9 and 6 respectively). Both subgroups of women with high restraint level (presenting either high or low disinhibition) consumed a diet with a lower energy density than subgroups of women with lower restraint level. Women with high restraint-low disinhibition had a lower consumption of red meat and processed meat and a lower consumption of diet soft drinks than women with low restraint-high disinhibition. They were also characterised by a higher intake of whole grains than women with high restraint-high disinhibition and than women with lower restraint level (with either high or low disinhibition). Women with high restraint-high disinhibition levels showed differences in dietary variables when compared with subgroups of women with lower restraint level, namely for refined grains and diet soft drinks. We conclude that in healthy postmenopausal women, dietary consumption of specific food and drink may be related to particular eating behaviours. Women with high restraint and low disinhibition levels generally showed the most healthy dietary pattern.     

Less traditional diets in Chinese mothers and children are similarly linked to socioeconomic and cohort factors but vary with increasing child age

Global shifts toward an increasingly Western diet and rises in nutrition-related noncommunicable diseases necessitate systematic examination of dietary change in adults and children. This study longitudinally examined mother and child dietary intakes and their relationship with socioeconomic factors across 4 mutually exclusive cohorts followed over 6- to 7-y time periods (cohort A: 1991-1997, cohort B: 1993-2000, cohort C: 1997-2004, cohort D: 2000-2006). The cohorts included 966 mother-child pairs (children 3-5 y at baseline) from the China Health and Nutrition Survey. Dietary intake was assessed using 24-h recall and household food consumption data; dietary variables were the percentage of total energy from animal-source foods (ASF), fats/oils, and grains. Mother-child comparison of dietary variables used average annual change measures, Spearman partial correlations, random effects models, and seemingly unrelated regression models and estimation. Whereas children were earlier adopters and maintainers of a less traditional Chinese diet, mothers experienced greater shifts away from the traditional Chinese diet with increasing child age. Mother-child correlations for the dietary variables ranged from 0.46 to 0.89 (P < 0.001). Similar increased intake of ASF and decreased intake of grains were reported for mothers and children of urban (vs. rural) residence and with higher levels of maternal education (P < 0.001). A comparable cohort effect was shown, with mothers and children consuming a less traditional Chinese diet in the later (C and D) compared to earlier (A and B) cohorts (P < 0.05). Our findings provide insight into dietary changes in mothers and children within the context of a rapidly changing nutrition and socioeconomic environment.     

Brain responses to high-protein diets

Proteins are suspected to have a greater satiating effect than the other 2 macronutrients. After protein consumption, peptide hormones released from the gastrointestinal tract (mainly anorexigenic gut peptides such as cholecystokinin, glucagon peptide 1, and peptide YY) communicate information about the energy status to the brain. These hormones and vagal afferents control food intake by acting on brain regions involved in energy homeostasis such as the brainstem and the hypothalamus. In fact, a high-protein diet leads to greater activation than a normal-protein diet in the nucleus tractus solitarius and in the arcuate nucleus. More specifically, neural mechanisms triggered particularly by leucine consumption involve 2 cellular energy sensors: the mammalian target of rapamycin and AMP-activated protein kinase. In addition, reward and motivation aspects of eating behavior, controlled mainly by neurons present in limbic regions, play an important role in the reduced hedonic response of a high-protein diet. This review examines how metabolic signals emanating from the gastrointestinal tract after protein ingestion target the brain to control feeding, energy expenditure, and hormones. Understanding the functional roles of brain areas involved in the satiating effect of proteins and their interactions will demonstrate how homeostasis and reward are integrated with the signals from peripheral organs after protein consumption.     

Low-fat diets and energy balance: how does the evidence stand in 2002?

The role of high-fat diets in weight gain and obesity is assessed by evidence-based principles. Four meta-analyses of weight change occurring on ad libitum low-fat diets in intervention trials consistently demonstrate a highly significant weight loss of 3-4 kg in normal-weight and overweight subjects (P < 0.001). The analyses also find a dose-response relationship, i.e. the reduction in percentage energy as fat is positively associated with weight loss. Weight loss is also positively related to initial weight; a 10 % reduction in dietary fat is predicted to produce a 4-5 kg weight loss in an individual with a BMI of 30 kg/m2. The non-fat macronutrient composition of the diet is also important. Whereas the glycaemic index of the carbohydrate may play a role for cardiovascular risk factors, there is so far no evidence that low-glycaemic index foods facilitate weight control. In contrast, intervention studies show that sugar in drinks is more likely to produce weight gain than solid sugar in foods. Although the evidence is weak, alcoholic beverages promote a positive energy balance, and wine may be more obesity-promoting than beer. Protein is more satiating and thermogenic than carbohydrates, and one intervention study has shown that an ad libitum low-fat diet where carbohydrate was replaced by protein produced more weight loss after 6 months (8.1 v. 5.9 kg). The evidence linking particular fatty acids to body fatness is weak. If anything, monounsaturated fat may be more fattening than polyunsaturated and saturated fats, and no ad libitum dietary intervention study has shown that a normal-fat high-monounsaturated fatty acid diet is equivalent or superior to a low-fat diet in the prevention of weight gain and obesity. The evidence strongly supports the low-fat diet as the optimal choice for the prevention of weight gain and obesity, while the use of a normal-fat high-monounsaturated fatty acid diet is unsubstantiated.     

Tobacco smoking, an independent determinant for unhealthy diet?: A cross-sectional study of Norwegian workers on platforms in the North Sea

The objective of the study was to examine whether male tobaccosmokers had a more unhealthy diet than non-smokers. Data onsmoking and other variables were collected by questionnaireinterviews and food intake by one 24 h recall. The setting was2 oll platforms. The participants were 310 healthy men workingon 2 platforms in the Norwegian sector of the North Sea. Themean ages were 37 and 39 years for non-smokers and smokers.The prevalence of smoking was 50.3%. Smoking decreased withincreasing level of education, but increased with degree ofurbanization. Smokers consumed less vegetables, fruit and fish,but more meat, soft drinks containing sugar and more coffeethan non-smokers. Smokers had a higher intake of fat and a lowerintake of carbohydrate, vitamins A, D and C and dietary fibre.Smoking was an independent predictor for increasing the consumptionof coffee and high intake of energy, energy from fat and cholesteroland a decreasing consumption of vegetables, fruit, energy fromcarbohydrates, dietary fibre and vitamins A and C. It is concludedthat smokers had a more unhealthy diet than non-smokers.     

Dietary fat and coronary heart disease: a comparison of approaches for adjusting for total energy intake and modeling repeated dietary measurements

Previous cohort studies of fat intake and risk of coronary heart disease (CHD) have been inconsistent, probably due in part to methodological differences and various limitations, including inadequate dietary assessment and incomplete adjustment for total energy intake. The authors analyzed repeated assessment of diet from the Nurses' Health Study to examine the associations between intakes of four major types of fat (saturated, monounsaturated, polyunsaturated, and trans fats) and risk of CHD during 14 years of follow-up (1980-1994) by using alternative methods for energy adjustment. In particular, the authors compared four risk models for energy adjustment: the standard multivariate model, the energy-partition model, the nutrient residual model, and the multivariate nutrient density model. Within each model, the authors compared four different approaches for analyzing repeated dietary measurements: baseline diet only, the most recent diet, and two different algorithms for calculating cumulative average diets. The substantive results were consistent across all models; that is, higher intakes of saturated and trans fats were associated with increased risk of CHD, while higher intakes of monounsaturated and polyunsaturated fats were associated with reduced risk. When nutrients were considered as continuous variables, the four energy-adjustment methods yielded similar associationS. However, the interpretation of the relative risks differed across models. In addition, within each model, the methods using the cumulative averages in general yielded stronger associations than did those using either only baseline diet or the most recent diet. When the nutrients were categorized according to quintiles, the residual and the nutrient density models, which gave similar results, yielded statistically more significant tests for linear trend than did the standard and the partition models.     

Sterol and nutrient excretion in ileostomists on prudent diets.

Nine ileostomists eating three diets (STAND, RESAT and EXFIB) were investigated in order to quantify the changes in sterol and nutrient excretion when shifting between a standard Western diet and two prudent diets. The RESAT diet had a moderate reduction in fat content to 30 per cent of energy, mainly through a reduction in saturated fat. The EXFIB diet had the same fat modification but in addition the dietary fibre content was raised to 3g/MJ according to current Swedish nutrition recommendations. The RESAT diet resulted in a lowered excretion of fat, but the excretion of nitrogen, energy, cholesterol and bile acids did not change compared with the STAND diet. The EXFIB diet resulted in a higher excretion of fat, nitrogen, energy and cholesterol compared with both the STAND and the RESAT diets (P less than 0.01). Bile acids showed no consistent excretion changes. Thus, a prudent diet, with moderate restricted total and saturated fat content, and a moderate increase in dietary fibre from natural food items, increased the excretion of cholesterol and fat from the small bowel when given to healthy ileostomists. A solely fat-modified prudent diet did not significantly change the pattern of excretion compared with a standard diet.     

Association between Ultra-processed Food Consumption and Dietary Intake and Diet Quality in Korean Adults

BackgroundFood environments have changed rapidly, and the global interest in ultra-processed foods has increased. Ultra-processed foods are typically energy dense, high in sugars and fat, and low in fiber, protein, minerals, and vitamins.ObjectiveThis study aimed to estimate the energy contribution of ultra-processed foods in the diet of Korean adults and to examine the association between ultra-processed food consumption and dietary intake and diet quality.DesignThis study is a secondary analysis of cross-sectional data from the Korea National Health and Nutrition Examination Survey (2016–2018).Participants/settingsA total of 16,657 adults aged ≥19 years who completed a 1-day 24-hour recall.Main outcome measuresAbsolute and relative intake of energy and nutrients were measured and dietary quality was assessed using the Korean Healthy Eating Index (KHEI).Statistical analysisMultiple regression models adjusted for sociodemographic variables were used to examine the association between quintiles of ultra-processed foods dietary energy contribution and dietary intake and quality.ResultsMean reported daily energy intake was 2,031 kcal, with 25.1% of calories coming from ultra-processed foods. Mean energy contribution from ultra-processed foods ranged from 3.6% kcal (Q1) to 52.4% kcal (Q5). Energy contribution of ultra-processed foods was positively associated with reported intake of daily energy, total sugars, and total and saturated fat and inversely associated with reported intake of carbohydrates, fiber, minerals, and vitamins. Both sodium and potassium were negatively associated with percentage of energy from ultra-processed foods. However, the sodium-to-potassium ratio was high regardless of quintile of energy contribution from ultra-processed foods, and the ratio was positively associated with percentage of total energy from ultra-processed foods. Although the KHEI score was inversely associated with percentage of daily energy from ultra-processed foods, all levels of ultra-processed food consumption were associated with poor diet quality.ConclusionsThe ultra-processed foods consumption of Korean adults accounted for one fourth of daily energy intake, and a higher dietary energy contribution from ultra-processed foods was associated with poorer dietary intakes and a lower dietary quality. Further studies are needed to understand factors influencing selection and consumption of ultra-processed foods and to identify effective strategies to promote healthy food choices.     

Dietary fiber and fat are associated with excess weight in young and middle-aged US adults

OBJECTIVE: To examine relative associations of dietary composition variables with body mass index (BMI; calculated as kg/m2) among young and middle-aged US adults. We hypothesized that in subjects with physiologically plausible reported energy intakes, fiber intake would be inversely associated with BMI, independent of other dietary composition and sociodemographic variables. SUBJECTS AND DESIGN: Data from adults age 20 to 59 years in the Continuing Survey of Food Intakes by Individuals (CSFII) 1994-1996 were used. Exclusions were pregnancy or lactation, food insecurity, missing weight or height data, or having only one dietary recall. Based on our previously published methods, a physiologically plausible reported energy intake was calculated as being within +/-22% of predicted energy requirements for the mean of two 24-hour recalls. RESULTS: Reporting plausibility ([reported energy intake/predicted energy requirements]x100) averaged 83% in the total sample (N=4,539) and increased to 96% in the plausible sample (n=1,932). Only approximately 5% of the plausible sample consumed the Adequate Intake for fiber. In plausibly reporting women, fiber, its interaction with percentage energy from fat, and energy density were independently associated with BMI. Only percentage energy from fat was associated with BMI in men reporting plausibly. Compared with the total sample, stronger relationships between diet and BMI were observed among the plausible reporters. In women, a low-fiber (< 1.5 g/MJ), high-fat (> or = 35% energy) diet was associated with the greatest increase in risk of overweight or obesity compared with a high-fiber, low-fat diet. CONCLUSIONS: Weight control advice for US women should place greater emphasis on consumption of fiber.     

Effect of fat-reduced diets on 24-h energy expenditure: comparisons between animal protein, vegetable protein, and carbohydrate

BACKGROUND: Single-meal tests have shown that protein has greater thermogenic and satiating effects than does carbohydrate, which may be relevant for the prevention and treatment of obesity if these effects can be maintained over 24 h. OBJECTIVE: The effects of pork-meat protein, soy protein, and carbohydrate on 24-h energy expenditure were compared. DESIGN: Twelve young, healthy, overweight and mildly obese [body mass index (in kg/m(2)): 26-32] nonsmoking men participated in a randomized, single-blind, 3-way crossover study lasting 4 d. The intervention had a 1-10-wk washout period. The 3 isoenergetic intervention diets were as follows: pork diet (29% of energy as fat and 29% as protein, mainly from pork meat), soy diet (29% of energy as fat and 28% as protein, mainly from soy), and carbohydrate diet (28% of energy as fat and 11% as protein). Twenty-four-hour energy expenditure was measured in a respiratory chamber at baseline and on day 4 of each intervention period. RESULTS: Twenty-four-hour energy expenditure was higher with the pork than with the soy (248 kJ/d, 1.9%; P: = 0.05) or carbohydrate (492 kJ/d, 3.9%; P: < 0.0001) diet and higher with the soy than with the carbohydrate (244 kJ/d, 1.9%; P: < 0.05) diet. However, because of a higher satiating effect, energy intake was 10-15% lower during the chamber stay than at baseline (P: > 0.05) with all 3 diets. The differences in energy expenditure remained unchanged after adjustment for differences in 24-h energy balance. CONCLUSIONS: Substitution of carbohydrate with 17-18% of energy as either pork-meat or soy protein produced a 3% higher 24-h energy expenditure. The animal protein in pork meat produced a 2% higher 24-h energy expenditure than did the vegetable protein in soy.     

A controlled high-fat diet induces an obese syndrome in rats

The prevalence of obesity is increasing. Although the etiology of obesity is complex, dietary factors, particularly the consumption of a high-fat (HF) diet, is considered a risk factor for its development. Nonetheless, a causal role of dietary fat has never been definitively documented, in part because of inadequate animal models. We developed a rat model of diet-induced obesity that will be a powerful tool for assessment of this issue. In four experiments, Long-Evans rats ate ad libitum a synthetic semipurified diet containing 20 g (HF) or 4 g [low-fat (LF)] of fat/100 g of diet or a nonpurified diet. Other rats ate ad libitum the HF diet in amounts matched to the energy intake of the LF rats. When compared over 10 wk of free feeding, HF rats weighed 10% more (P < 0.01) than LF rats and had 50% more body fat (P < 0.01), as well as significant hyperleptinemia and insulin resistance. Compared with rats fed the nonpurified diet, the HF rats had even more marked differences in these variables. The rats fed the HF diet to match the rats fed the LF diet had similar body weights but significantly more adipose tissue than LF rats, suggesting that diet composition and/or energy density of the diet affects fat deposition. This dietary regimen has reproducible effects on body size and composition, and these are similar in male and female rats. This model of diet-induced obesity will be a useful tool for studying the mechanisms by which dietary fat influences the regulation of energy balance.     

Poverty and obesity: the role of energy density and energy costs

Many health disparities in the United States are linked to inequalities in education and income. This review focuses on the relation between obesity and diet quality, dietary energy density, and energy costs. Evidence is provided to support the following points. First, the highest rates of obesity occur among population groups with the highest poverty rates and the least education. Second, there is an inverse relation between energy density (MJ/kg) and energy cost (US dollars/MJ), such that energy-dense foods composed of refined grains, added sugars, or fats may represent the lowest-cost option to the consumer. Third, the high energy density and palatability of sweets and fats are associated with higher energy intakes, at least in clinical and laboratory studies. Fourth, poverty and food insecurity are associated with lower food expenditures, low fruit and vegetable consumption, and lower-quality diets. A reduction in diet costs in linear programming models leads to high-fat, energy-dense diets that are similar in composition to those consumed by low-income groups. Such diets are more affordable than are prudent diets based on lean meats, fish, fresh vegetables, and fruit. The association between poverty and obesity may be mediated, in part, by the low cost of energy-dense foods and may be reinforced by the high palatability of sugar and fat. This economic framework provides an explanation for the observed links between socioeconomic variables and obesity when taste, dietary energy density, and diet costs are used as intervening variables. More and more Americans are becoming overweight and obese while consuming more added sugars and fats and spending a lower percentage of their disposable income on food.     

The effect of correlated measurement error in multivariate models of diet

Self-reported diet is prone to measurement error. Analytical models of diet may include several foods or nutrients to avoid confounding. Such multivariate models of diet may be affected by errors correlated among the dietary covariates, which may introduce bias of unpredictable direction and magnitude. The authors used 1993-1998 data from the European Prospective Investigation into Cancer and Nutrition in Norfolk, United Kingdom, to explore univariate and multivariate regression models relating nutrient intake estimated from a 7-day diet record or a food frequency questionnaire to plasma levels of vitamin C. The purpose was to provide an empirical examination of the effect of two different multivariate error structures in the assessment of dietary intake on multivariate regression models, in a situation where the underlying relation between the independent and dependent variables is approximately known. Emphasis was put on the control for confounding and the effect of different methods of controlling for estimated energy intake. The results for standard multivariate regression models were consistent with considerable correlated error, introducing spurious associations between some nutrients and the dependent variable and leading to instability of the parameter estimates if energy was included in the model. Energy adjustment using regression residuals or energy density models led to improved parameter stability.     

No differences in satiety or energy intake after high-fructose corn syrup, sucrose, or milk preloads

BACKGROUND: It is unclear whether energy-containing drinks, especially those sweetened with high-fructose corn syrup (HFCS), promote positive energy balance and thereby play a role in the development of obesity. OBJECTIVE: The objective was to examine the satiating effects of HFCS and sucrose in comparison with milk and a diet drink. DESIGN: The effects of four 800-mL drinks [corrected] containing no energy or 1.5 MJ from sucrose, HFCS, or milk on satiety were assessed, first in 15 men and 15 women with a mean (+/-SD) body mass index (BMI; in kg/m(2)) of 22.1 +/- 1.9 according to visual analogue scales (VAS) and blood variables and second in 20 men and 20 women (BMI: 22.4 +/- 2.1) according to ingestion of a standardized ad libitum meal (granola cereal + yogurt, 10.1 kJ/g). RESULTS: Fifty minutes after consumption of the 1.5-MJ preload drinks containing sucrose, HFCS, or milk, 170%-mm VAS changes in satiety were observed. Glucagon-like peptide 1 (GLP-1) (P < 0.001) and ghrelin (P < 0.05) concentrations changed accordingly. Compensatory energy intake did not differ significantly between the 3 preloads and ranged from 30% to 45%. Energy intake compensations were related to satiety (r = 0.35, P < 0.05). No differences were observed between the effects of the sucrose- and HFCS-containing drinks on changes in VAS and on insulin, glucose, GLP-1, and ghrelin concentrations. Changes in appetite VAS ratings were a function of changes in GLP-1, ghrelin, insulin, and glucose concentrations. CONCLUSION: Energy balance consequences of HFCS-sweetened soft drinks are not different from those of other isoenergetic drinks, eg, a sucrose-drink or milk.