Knee strength maintained despite loss of lean body mass during weight loss in older obese adults with knee osteoarthritis

BACKGROUND: The effects of weight loss on muscle function in older adults have not been well studied. This study determined the effects of a 6-month weight-loss intervention on muscle strength and quality in older obese adults with knee osteoarthritis. METHODS: Participants were randomized to a weight loss (WL) (n = 44, 70 +/- 6 years) or weight stable (WS) (n = 43, 69 +/- 6 years) group. The WL intervention consisted of weekly educational meetings, a meal replacement diet, and a three-session-per-week structured exercise program to achieve 10%-12% weight loss. The WS intervention included bimonthly group meetings and newsletters. Body composition and knee extensor strength were measured at baseline and after intervention. RESULTS: The WL group decreased body weight, lean body mass, fat mass, and percent body fat (p <.001 for all). Concentric extension strength increased 25% in WL (p >.05), whereas eccentric extension decreased 6% in WS (p =.028). Concentric muscle quality (strength per kg body weight or lean body mass) increased in WL (p <.05), whereas eccentric muscle quality decreased in WS (p <.05). Changes in lean body mass and fat mass were inversely associated with changes in most muscle strength and quality measures (p <.05). Men and women did not differ in response to the intervention in knee strength outcomes. CONCLUSIONS: Hypocaloric dieting in combination with exercise training had beneficial effects on muscle strength/quality, despite loss of lean body mass in this sample of older men and women. Greater fat loss was associated with greater gains in muscle strength and quality. More studies are needed regarding the mechanisms by which loss of fat mass increases muscle strength and quality.     

Low-fat, high-carbohydrate (low-glycaemic index) diet induces weight loss and preserves lean body mass in obese healthy subjects: results of a 24-week study

BACKGROUND: The traditional treatment for obesity which is based on a reduced caloric diet has only been partially successful. Contributing factors are not only a poor long-term dietary adherence but also a significant loss of lean body mass and subsequent reduction in energy expenditure. Both low-fat, high-carbohydrate diets and diets using low-glycaemic index (GI) foods are capable of inducing modest weight loss without specific caloric restriction. The purpose of this study was to investigate the feasibility and medium-term effect of a low-fat diet with high (low GI) carbohydrates on weight loss, body composition changes and dietary compliance. METHODS: Obese patients were recruited from two obesity outpatient clinics. Subjects were given advise by a dietician, then they attended biweekly for 1-hour group meetings. Bodyweight and body composition were measured at baseline and after 24 weeks. RESULTS: One hundred and nine (91%) patients completed the study; after 24 weeks the average weight loss was 8.9 kg (98.6 vs. 89.7 kg; p < or = 0.0001). There was a significant 15% decrease in fat mass (42.5 vs. 36.4 kg; p < or = 0.0001) and a decrease in lean body mass of 5% (56.1 vs. 53.3 kg; p < or = 0.0001). DISCUSSION: In this 6-month study, a low-fat, low-GI diet led to a significant reduction of fat mass; adherence to the diet was very good. Our results suggest that such a diet is feasible and should be evaluated in randomized controlled trials.     

Effect of calcium and dairy foods in high protein, energy-restricted diets on weight loss and metabolic parameters in overweight adults

OBJECTIVE: To compare the effects two high-protein (HP) diets that differ in dietary calcium and protein source on weight loss, body composition, glucose and lipid metabolism, markers of liver function, fibrinolysis and endothelial function and blood pressure. DESIGN: Randomized, parallel study (12 wk of energy restriction, 4 wk of energy balance) of high dairy protein/high-calcium (DP, 2400 mg Ca/d) and high mixed protein/moderate calcium (MP, 500 mg Ca/d) diets (5.5 MJ/d, 34% protein, 41% carbohydrate, 24% fat). SUBJECTS: In all, 50 healthy, overweight (age 25-64 y; body mass index 25-35 kg/m(2);) males (n=20) and females (n=30). RESULTS: Loss of total weight (-9.7+/-3.8 kg), fat mass (-8.3+/-0.4 kg) and lean mass (-1.6+/-0.3 kg) were independent of dietary group. Improvements in fasting insulin, lipids, systolic/diastolic blood pressure, and markers of liver function, fibrinolysis and endothelial function were independent of dietary intervention. CONCLUSIONS: Increased dietary calcium/dairy foods in an energy-restricted, HP diet does not affect weight loss or body composition. Weight reduction following increased protein diets is associated with beneficial metabolic outcomes that are not affected by protein source.     

Weight loss composition is one‐fourth fat‐free mass: a critical review and critique of this widely cited rule

Maximizing fat loss while preserving lean tissue mass and function is a central goal of modern obesity treatments. A widely cited rule guiding expected loss of lean tissue as fat‐free mass (FFM) states that approximately one‐fourth of weight loss will be FFM (i.e. ΔFFM/ΔWeight = ～0.25), with the remaining three‐fourths being fat mass. This review examines the dynamic relationships between FFM, fat mass and weight changes that follow induction of negative energy balance with hypocaloric dieting and/or exercise. Historical developments in the field are traced with the ‘Quarter FFM Rule’ used as a framework to examine evolving concepts on obesity tissue, excess weight and what is often cited as ‘Forbes' Rule’. Temporal effects in the fractional contribution of FFM to changes in body weight are examined as are lean tissue moderating effects such as ageing, inactivity and exercise that frequently accompany structured low‐calorie diet weight loss protocols. Losses of lean tissue with dieting typically tend to be small, raising questions about study design, power and applied measurement method reliability. Our review elicits important questions related to the fractional loss of lean tissues with dieting and provides a foundation for future research on this topic.     

Effects of acetylenedicarboxylate: relationship between decreased carcass lipid and increased liver size and lean body weight.

Potassium acetylenedicarboxylate, when administered in the diet, reduced the body lipid content of normal mice, genetically obese (ob/ob) mice, and their lean (+/?) littermates, and mice made obese by treatment with goldthioglucose. Food intake was unchanged in the lean mice but decreased in the obese mice. Carcass lipid was decreased in genetically obese mice compared to pair-fed controls. Oxygen consumption per mouse was increased in normal mice. The reduction in carcass lipid was not produced in normal mice that were dosed orally or were fed on a diet containing 55 per cent sucrose. Nor was it produced in male castrated mice or streptozotocin-treated mice that were given daily injections of insulin. The reduction in body lipid weight in lean mice was correlated with an increase in liver weight. Liver weight was not increased in genetically obese mice, but there was an increase in lipid-free dry weight. Weight gain was increased in lean mice and decreased in the obese mice compared to ad lib-fed controls. A red colouration of the skin developed in situations where body lipid content was decreased; plasma histamine was increased in lean mice. It is proposed that increased histamine synthesis leads to increased protein turnover and decreased body lipid content.     

Effects of weight loss on body composition and pulmonary function.

BACKGROUND: The relationship between obesity, impaired respiratory function and weight loss is established. OBJECTIVE: Some aspects need further elucidation: the different impact of the pathological modifications of body compartments (total and regional fat mass and lean body mass) on respiratory function, the choice of a restricted diet, the relationship between the modifications of body compartments and the variations in respiratory parameters after weight loss. METHODS: The restricted diet was elaborated according to the traditional Mediterranean diet. In a series of 16 obese patients, respiratory function was assessed by spirometry; body composition was assessed by dual-energy X-ray absorptiometry, allowing the direct estimation of total and segmental body fat and lean body mass. RESULTS: Weight loss was sustained mainly by fat mass decrease, mostly upper body fat. Total and truncal lean body mass were not affected. Lung volumes and function were improved. A correlation was observed between lean body mass and respiratory parameters, and was unmodified after weight loss. CONCLUSIONS: Mediterranean-style restricted diet was well accepted and enabled a selective decrease in fat mass, with a good improvement in lung function. Truncal fat (as well as abdominal fat) was decreased, while truncal lean body mass (i.e. respiratory muscles) were not affected, as expected in obese subjects with respiration problems.     

Subcutaneous adipose tissue cytokine production is not responsible for the restoration of systemic inflammation markers during weight loss

CONTEXT: It has been suggested that weight loss can improve systemic inflammation associated with obesity by decreasing the adipose production of pro-inflammatory cytokines. This suggestion, however, remains controversial. OBJECTIVE: To analyse the effect of weight loss on peripheral inflammatory markers and subcutaneous adipocytokine production. DESIGN: Patients were studied at baseline, at the end of the weight loss period, and after 2 weeks of weight stabilisation. SUBJECTS: Nineteen morbid obese non-diabetic patients and 20 lean control subjects. INTERVENTION: During the weight loss period patients followed a 6-week low-calorie diet. MEASUREMENTS: Plasma levels of inflammatory markers, maximal in vitro whole-blood cytokine production, subcutaneous adipose tissue expression and content of several cytokines. RESULTS: Obese subjects had higher circulating levels of C reactive protein (CRP), serum amyloid A (SAA), interleukin IL-6, IL-1 and soluble tumor necrosis factor receptors (sTNFR). Weight loss was associated with a significant decrease in CRP, SAA, leucocytes and plasma IL-6. Maximal in vitro cytokine production of IL-1 and sTNFR1 increased during this period. Weight loss did not induce significant changes in the adipose concentrations of IL-6, IL-1 or sTNF-receptors. However, adipose expression of IL-6, IL-1, TNFalpha, membrane cofactor protein-1 and adiponectin increased at the end of the weight loss period. During weight maintenance, circulating inflammatory parameters increased and in some cases returned to baseline. CONCLUSIONS: A low-calorie diet is associated with an improvement in the systemic inflammatory status. This seems to be due to energy restriction rather than to adipose mass loss, since inflammatory levels return to baseline soon after weight stabilisation. Furthermore, a negative energy balance and fat mobilisation are associated with increased subcutaneous cytokine adipose expression.     

Rat strain specific attenuation of estrogen action in the anterior pituitary gland by dietary energy restriction

The purpose of this study was to compare the effects of a 40% restriction of dietary energy consumption, relative to that consumed by rats allowed to feed ad libitum, on the ability of 17β-estradiol (E2) to induce pituitary tumorigenesis in two inbred rat strains, ACI and Copenhagen (COP), which are very closely related genetically. Ovary-intact ACI and COP rats were fed either a control or an energy-restricted diet beginning at 8 wk of age. Continuous treatment with E2, released from subcutaneous Silastic tubing implants, was initiated at 9 wk of age and the animals were killed 12 wk later. Estrogen-induced pituitary tumorigenesis is associated with rapid induction of lactotroph hyperplasia, increased pituitary mass, and hyperprolactinemia. E2 significantly increased pituitary mass and circulating prolactin (PRL) in both ACI and COP rats, and this response was significantly greater in ACI rats relative to COP. Dietary energy restriction did not inhibit E2-induced pituitary growth in the ACI rat. By contrast, E2-induced pituitary growth in COP rats was attenuated by dietary energy restriction, as evidenced by quantification of pituitary mass, pituitary weight to body weight ratio, circulating PRL, and pituitary cell proliferation. This study indicates that sensitivity to the inhibitory actions of dietary energy restriction on E2-induced pituitary tumorigenesis is genetically determined.     

Nitrogen balances of lean and obese Zucker rats subjected to a cafeteria diet.

The effects of a cafeteria diet on nitrogen balance in lean (Fa/?) and obese Zucker rats (fa/fa) was studied for two consecutive 15 day periods after weaning. Obese rats were able to absorb a lower proportion of dietary nitrogen than the lean controls. Cafeteria diet increased the retention of dietary nitrogen, and lowered urinary nitrogen losses in both obese and lean rats. Urea constituted practically the only product of urinary nitrogen excretion in obese rats, whereas it accounted for only about 75% of that eliminated by Fa/? rats. Nitrogen accretion in the body was highest for the younger animals, and again increased with cafeteria feeding. Obese fa/fa rats showed a lower percentage of body nitrogen retention than their lean counterparts; obese rats were able, however, to accumulate large amounts of nitrogen and fat, in part because of their higher intake. A significant part of the absorbed nitrogen was not found in either the body or the urine; the cafeteria diet markedly increased the weight of this fraction of nitrogen unaccounted for. In conclusion, the effects of cafeteria feeding on weight and nitrogen handling were comparable in lean and obese rats, i.e. the effects of genetic and dietary obesity seem to be additive with regard to nitrogen extraction and excretion for Zucker rats.     

Adherence to a low‐fat vs. low‐carbohydrate diet differs by insulin resistance status

Previous research shows diminished weight loss success in insulin‐resistant (IR) women assigned to a low‐fat (LF) diet compared to those assigned to a low‐carbohydrate (LC) diet. These secondary analyses examined the relationship between insulin‐resistance status and dietary adherence to either a LF‐diet or LC‐diet among 81 free‐living, overweight/obese women [age = 41.9 ± 5.7 years; body mass index (BMI) = 32.6 ± 3.6 kg/m²]. This study found differential adherence by insulin‐resistance status only to a LF‐diet, not a LC‐diet. IR participants were less likely to adhere and lose weight on a LF‐diet compared to insulin‐sensitive (IS) participants assigned to the same diet. There were no significant differences between IR and IS participants assigned to LC‐diet in relative adherence or weight loss. These results suggest that insulin resistance status may affect dietary adherence to weight loss diets, resulting in higher recidivism and diminished weight loss success of IR participants advised to follow LF‐diets for weight loss.     

Body composition and hormonal responses to a carbohydrate-restricted diet

The few studies that have examined body composition after a carbohydrate-restricted diet have reported enhanced fat loss and preservation of lean body mass in obese individuals. The role of hormones in mediating this response is unclear. We examined the effects of a 6-week carbohydrate-restricted diet on total and regional body composition and the relationships with fasting hormone concentrations. Twelve healthy normal-weight men switched from their habitual diet (48% carbohydrate) to a carbohydrate-restricted diet (8% carbohydrate) for 6 weeks and 8 men served as controls, consuming their normal diet. Subjects were encouraged to consume adequate dietary energy to maintain body mass during the intervention. Total and regional body composition and fasting blood samples were assessed at weeks 0, 3, and 6 of the experimental period. Fat mass was significantly (P 相似文献   

Good Calories, Bad Calories by Gary Taubes; New York: AA Knopf

Good Calories, Bad Calories has much useful information and is well worth reading. Gary Taubes's tenets related to obesity can be summarized in four statements (i) He believes that you can gain weight and become obese without a positive energy balance; (ii) He also believes that dietary fat is unimportant for the development of obesity; (iii) Carbohydrate, in his view, is what produces obesity and (iv) Insulin secreted by the carbohydrate is the problem in obesity. However, some of the conclusions that the author reaches are not consistent with current concepts about obesity. There are many kinds of obesity, and only some depend on diet composition. Two dietary manipulations produce obesity in susceptible people: eating a high‐fat diet and drinking sugar‐ or high‐fructose corn syrup‐sweetened beverages. Insulin is necessary but not sufficient in the diet‐dependent obesities. When diet is important, it may be the combination of fat and fructose (the deadly duo) that is most important. Regardless of diet, it is a positive energy balance over months to years that is the sine qua non for obesity. Obese people clearly eat more than do lean ones, and food‐intake records are notoriously unreliable, as documented by use of doubly labelled water. Underreporting of food intake is greater in obese than in normal‐weight people and is worse for fat than for other macronutrient groups. Accepting the concept that obesity results from a positive energy balance does not tell us why energy balance is positive. This depends on a variety of environmental factors interacting with the genetic susceptibility of certain individuals. Weight loss is related to adherence to the diet, not to its macronutrient composition.     

Soluble activin receptor type IIB treatment does not cause fat loss in mice with diet-induced obesity

The growth factor myostatin (MSTN) negatively regulates skeletal muscle mass. Mstn gene deletion in mice causes increased muscle mass, reduced adiposity and resistance to genetic or diet-induced obesity (DIO). Pharmacologic MSTN inhibition in mice also causes increased muscle mass and resistance to DIO. To test whether MSTN inhibition causes weight loss in mice that are already obese, we inhibited MSTN in mice fed a high-fat diet (HFD). Mice were fed a diet containing 60% kcal from fat for 12 weeks followed by treatment with a soluble MSTN receptor derived from the activin receptor type IIB extracellular domain. During the next 12 weeks of soluble receptor treatment and HFD feeding, lean mass increased without a loss of adipose mass. Glucose metabolism was also similar between groups. Our results suggest that MSTN inhibition may be ineffective at inducing weight loss in obese patients.     

Weight reduction for treatment of obesity-associated hypertension: Nuances and challenges

Weight reduction is generally recommended as the first line of treatment for the increasing problem of obesity-associated hypertension. At first glance, this recommendation seems compelling, but evidence suggests that weight loss for obesity-associated hypertension is neither simple nor consistently effective as antihypertensive therapy. First, dietary and behavioral therapy is accompanied by an extremely high rate of weight regain after loss. Mounting evidence shows that this recidivism reflects neurobiologic and not simply psychologic adaptations to dietary restriction. Second, chronic blood pressure-lowering effects of weight loss produced by diet, weight-reducing drugs, or bariatric surgery may not be as pronounced as commonly thought. Third, there is evidence that dietary restriction, independent of weight loss, reduces sympathetic nervous system activity and might thereby contribute to reducing blood pressure. This phenomenon deserves more consideration in designing and interpreting studies of blood pressure changes during diet-induced weight loss. This article reviews these issues and highlights the nuances and challenges in the effectiveness of weight loss for treatment of obesity-induced hypertension.     

Age-related changes in body composition of bovine growth hormone transgenic mice

GH has a significant impact on body composition due to distinct anabolic and catabolic effects on lean and fat mass, respectively. Several studies have assessed body composition in mice expressing a GH transgene. Whereas all studies report enhanced growth of transgenic mice as compared with littermate controls, there are inconsistencies in terms of the relative proportion of lean mass to fat mass in these animals. The purpose of this study was to characterize the accumulation of adipose and lean mass with age and according to gender in a bovine (b) GH transgenic mouse line. Weight and body composition measurements were assessed in male and female bGH mice with corresponding littermate controls in the C57BL/6J genetic background. Body composition measurements began at 6 wk and continued through 1 yr of age. At the conclusion of the study, tissue weights were determined and triglyceride content was quantified in liver and kidney. Although body weights for bGH mice were significantly greater than their corresponding littermate controls at all time points, body composition measurements revealed an unexpected transition midway through analyses. That is, younger bGH mice had relatively more fat mass than nontransgenic littermates, whereas bGH mice became significantly leaner than controls by 4 months in males and 6 months in females. These results reveal the importance in timing and gender when conducting studies related to body composition or lean and fat tissue in GH transgenic mice or in other genetically manipulated mouse strains in which body composition may be impacted.     

Long term weight maintenance after advice to consume low carbohydrate,higher protein diets – A systematic review and meta analysis

BackgroundMeta analysis of short term trials indicates that a higher protein, lower carbohydrate weight loss diet enhances fat mass loss and limits lean mass loss compared with a normal protein weight loss diet. Whether this benefit persists long term is not clear.Methods and resultsWe selected weight loss studies in adults with at least a 12 month follow up in which a higher percentage protein/lower carbohydrate diet was either planned or would be expected for either weight loss or weight maintenance. Studies were selected regardless of the success of the advice but difference in absolute and percentage protein intake at 12 months was used as a moderator in the analysis. Data was analysed using Comprehensive Meta analysis V2 using a random effects analysis. As many as 32 studies with 3492 individuals were analysed with data on fat and lean mass, glucose and insulin from 18 to 22 studies and lipids from 28 studies. A recommendation to consume a lower carbohydrate, higher protein diet in mostly short term intensive interventions with long term follow up was associated with better weight and fat loss but the effect size was small-standardised means of 0.14 and 0.22, p = 0.008 and p < 0.001 respectively (equivalent to 0.4 kg for both). A difference of 5% or greater in percentage protein between diets at 12mo was associated with a 3 fold greater effect size compared with <5% (p = 0.038) in fat mass (0.9 vs. 0.3 kg). Fasting triglyceride and insulin were also lower with high protein diets with effect sizes of 0.17 and 0.22, p = 0.003 and p = 0.042 respectively. Other lipids and glucose were not different.ConclusionThe short term benefit of higher protein diets appears to persist to a small degree long term. Benefits are greater with better compliance to the diet.     

Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?

Dietary restriction is an effective strategy for weight loss in obese individuals. The most common form of dietary restriction implemented is daily calorie restriction (CR), which involves reducing energy by 15–60% of usual caloric intake every day. Another form of dietary restriction employed is intermittent CR, which involves 24 h of ad libitum food consumption alternated with 24 h of complete or partial food restriction. Although both diets are effective for weight loss, it remains unknown whether one of these interventions produces superior changes in body weight and body composition when compared to the other. Accordingly, this review examines the effects of daily CR versus intermittent CR on weight loss, fat mass loss and lean mass retention in overweight and obese adults. Results reveal similar weight loss and fat mass loss with 3 to 12 weeks' intermittent CR (4–8%, 11–16%, respectively) and daily CR (5–8%, 10–20%, respectively). In contrast, less fat free mass was lost in response to intermittent CR versus daily CR. These findings suggest that these diets are equally as effective in decreasing body weight and fat mass, although intermittent CR may be more effective for the retention of lean mass.     

The satiating effect of dietary protein is unrelated to postprandial ghrelin secretion

CONTEXT: Increasing dietary protein relative to carbohydrate and fat enhances weight loss, at least in part by increasing satiety. The mechanism for this is unclear. OBJECTIVE: The objective of this study was to compare the effects of isocaloric test meals with differing protein to fat ratios on fasting and postprandial ghrelin, insulin, glucose, appetite, and energy expenditure before and after weight loss on the respective dietary patterns. DESIGN: The study design was a randomized parallel design of 12 wk of weight loss (6 MJ/d) and 4 wk of weight maintenance (7.3 MJ/d) with meals administered at wk 0 and 16. SETTING: The study was performed at an out-patient research clinic. PATIENTS AND OTHER PARTICIPANTS: Fifty-seven overweight (body mass index, 33.8 +/- 3.5 kg/m2) hyperinsulinemic men (n = 25) and women (n = 32) were studied. Interventions: High-protein/low-fat (34% protein/29% fat) or standard protein/high-fat (18% protein/45% fat) diets/meals were given. MAIN OUTCOME MEASURES: The main outcome measures were weight loss and fasting and postprandial ghrelin, insulin, glucose, appetite, and energy expenditure before and after weight loss. RESULTS: Weight loss (9.2 +/- 0.7 kg) and improvements in fasting and postprandial insulin and glucose occurred independently of diet composition. At wk 0 and 16, subjects wanted less to eat after the high-protein/low-fat than the standard protein/high-fat meal (P = 0.02). Fasting ghrelin increased (157.5 +/- 3.4 pg/ml or 46.6 +/- 1.0 pmol/liter; P < 0.001), and the postprandial ghrelin response improved with weight loss (P = 0.043) independently of diet composition. Postprandial hunger decreased with weight loss (P = 0.018) and was predicted by changes in fasting and postprandial ghrelin (r2 = 0.246; P = 0.004). Lean mass was the best predictor of fasting (r2 = 0.182; P = 0.003) and postprandial ghrelin (r2 = 0.096; P = 0.039) levels. CONCLUSIONS: Exchanging protein for fat produced similar weight loss and improvements in metabolic parameters and ghrelin homeostasis. The reduced appetite observed with increased dietary protein appears not to be mediated by ghrelin homeostasis.