Randomised controlled trials comparing low- v. high-fat diets on cardiometabolic risk factors in people with overweight or obesity have shown inconsistent results, which may be due to the mixed metabolic status of people with excess adiposity. The role of dietary fat manipulation in modifying cardiometabolic indicators in people with overweight or obese without metabolic disturbance is unclear. Thus, meta-analysis was conducted to compare low- v. high-fat diets on cardiometabolic indicators in people who are overweight or obese without metabolic disturbance in the present study. Databases were searched until October 2016. The pooled effects of outcomes with heterogeneity were calculated with a random-effects model, heterogeneities were analysed by subgroup and meta-regression. As a result, twenty studies with 2106 participants were included in the meta-analysis. Total cholesterol and LDL-cholesterol levels were lower following low-fat diets compared with high-fat diets: weighted mean difference (WMD) was −7·05 mg/dl (−0·18 mmol/l; 95 % CI −11·30, −2·80; P=0·001) and −4·41 mg/dl (−0·11 mmol/l; 95 % CI −7·81, −1·00; P=0·011), respectively. Conversely, significant higher level of TAG (WMD: 11·68 mg/dl (0·13 mmol/l), 95 % CI 5·90, 17·45; P<0·001) and lower level of HDL-cholesterol (WMD: −2·57 mg/dl (−0·07 mmol/l); 95 % CI −3·85, −1·28; P<0·001) were found following low-fat diets compared with high-fat diets. In conclusion, dietary fat manipulation has a significant influence on blood lipid levels in people with overweight or obesity without metabolic disturbances.

It is unclear which of four popular contemporary diet patterns is best for weight maintenance among postmenopausal women. Four dietary patterns were characterised among postmenopausal women aged 49–81 years (mean 63·6 (sd 7·4) years) from the Women’s Health Initiative Observational Study: (1) a low-fat diet; (2) a reduced-carbohydrate diet; (3) a Mediterranean-style (Med) diet; and (4) a diet consistent with the US Department of Agriculture’s Dietary Guidelines for Americans (DGA). Discrete-time hazards models were used to compare the risk of weight gain (≥10 %) among high adherers of each diet pattern. In adjusted models, the reduced-carbohydrate diet was inversely related to weight gain (OR 0·71; 95 % CI 0·66, 0·76), whereas the low-fat (OR 1·43; 95 % CI 1·33, 1·54) and DGA (OR 1·24; 95 % CI 1·15, 1·33) diets were associated with increased risk of weight gain. By baseline weight status, the reduced-carbohydrate diet was inversely related to weight gain among women who were normal weight (OR 0·72; 95 % CI 0·63, 0·81), overweight (OR 0·67; 95 % CI 0·59, 0·76) or obese class I (OR 0·63; 95 % CI 0·53, 0·76) at baseline. The low-fat diet was associated with increased risk of weight gain in women who were normal weight (OR 1·28; 95 % CI 1·13, 1·46), overweight (OR 1·60; 95 % CI 1·40, 1·83), obese class I (OR 1·73; 95 % CI 1·43, 2·09) or obese class II (OR 1·44; 95 % CI 1·08, 1·92) at baseline. These findings suggest that a low-fat diet may promote weight gain, whereas a reduced-carbohydrate diet may decrease risk of postmenopausal weight gain.

The effects of low-carbohydrate (LC) diets on body weight and cardiovascular risk are unclear, and previous studies have found varying results. Our aim was to conduct a meta-analysis of randomised controlled trials (RCT), assessing the effects of LC diets v. low-fat (LF) diets on weight loss and risk factors of CVD. Studies were identified by searching MEDLINE, Embase and Cochrane Trials. Studies had to fulfil the following criteria: a RCT; the LC diet was defined in accordance with the Atkins diet, or carbohydrate intake of <20 % of total energy intake; twenty subjects or more per group; the subjects were previously healthy; and the dietary intervention had a duration of 6 months or longer. Results from individual studies were pooled as weighted mean difference (WMD) using a random effect model. In all, eleven RCT with 1369 participants met all the set eligibility criteria. Compared with participants on LF diets, participants on LC diets experienced a greater reduction in body weight (WMD –2·17 kg; 95 % CI –3·36, –0·99) and TAG (WMD –0·26 mmol/l; 95 % CI –0·37, –0·15), but a greater increase in HDL-cholesterol (WMD 0·14 mmol/l; 95 % CI 0·09, 0·19) and LDL-cholesterol (WMD 0·16 mmol/l; 95 % CI 0·003, 0·33). This meta-analysis demonstrates opposite change in two important cardiovascular risk factors on LC diets – greater weight loss and increased LDL-cholesterol. Our findings suggest that the beneficial changes of LC diets must be weighed against the possible detrimental effects of increased LDL-cholesterol.

The aim of the present systematic review and meta-analysis was to examine the long-term effects ( ≥ 12 months) of high-fat (HF) v. low-fat (LF) diet consumption on the indicators of glycaemic control as well as cardiovascular risk factors in pre-diabetic and diabetic individuals. Literature search was carried out using the electronic databases MEDLINE, Embase and the Cochrane Trial Register until November 2013. Study-specific weighted mean differences (MD) were pooled using a random-effects model of the Cochrane software package Review Manager 5.1 and Stata 12.0 was used for meta-regressions. A total of fourteen trials met the inclusion criteria and a maximum of 1753 subjects were included in the meta-analysis. HF regimens were found to result in a significant decrease in TAG levels (MD − 0·19 mmol/l, 95 % CI − 0·23, − 0·14, P< 0·001; I2= 0 %, P= 0·58) and diastolic blood pressure (MD − 1·30 mmHg, 95 % CI − 1·73, − 0·87, P< 0·001; I2= 0 %, P= 0·60) and a significant increase in HDL-cholesterol levels (MD 0·05 mmol/l, 95 % CI 0·01, 0·08, P= 0·01; I2= 57 %, P= 0·01). In addition, MD in the reductions of fasting glucose levels ( − 0·41 mmol/l, 95 % CI − 0·74, − 0·08, P= 0·01; I2= 56 %, P= 0·02) were significantly high in patients with type 2 diabetes adhering to a HF diet. HF and LF diets might not be of equal value in the management of either pre-diabetes or type 2 diabetes, leading to emphasis being placed on the recommendations of HF diets.

The aim of the present study was to compare the long-term effects of two dietary approaches on changes in dietary intakes, eating behaviours and body weight: (1) approach using restrictive messages to limit high-fat foods (low-fat intake; LOFAT); (2) approach emphasising non-restrictive messages directed towards the inclusion of fruits and vegetables (high intake of fruits and vegetables; HIFV). A total of sixty-eight overweight or obese postmenopausal women were randomly assigned to one of the two dietary approaches. The 6-month dietary intervention included three group sessions and ten individual sessions with a dietitian. Dietary intakes, eating behaviours and anthropometrics were measured at baseline, at the end of the dietary intervention (T = 6) and 6 months and 12 months after the end of the intervention (T = 12 and T = 18). In the LOFAT group, energy and fat intakes were lower at T = 6 when compared with baseline and remained lower at T = 12 and T = 18. In the HIFV group, fruit and vegetable intakes increased significantly at T = 6 but were no longer significantly different from baseline at T = 12 and T = 18. Dietary restraint increased at T = 6 and remained higher than baseline at T = 18 in the LOFAT group while no significant change was observed in the HIFV group. At T = 6, body weight was significantly lower than baseline in both groups (LOFAT: − 3·7 (sd 2·8) kg; HIFV: − 1·8 (sd 3·0) kg) and no significant difference in body-weight change from baseline was found between groups at T = 18. We concluded that weight loss was similar at 1-year follow-up in both dietary approaches. Despite relatively good improvements in the short term, the adherence to a 6-month dietary intervention promoting high intakes of fruits and vegetables was difficult to maintain.

To evaluate the efficacy of adding cognitive behavioural treatment (CBT) to either a low-carbohydrate (LC) diet or a low-fat (LF) diet in the treatment of weight loss of obese women, a randomised clinical intervention study was performed. A total of 105 healthy non-pregnant obese women (average age and BMI of 45·4 (sd 10·4) years and 36 (sd 4·3) kg/m2) were randomly allocated to the CBT or control (C) groups; within each group, women were randomly selected to receive either the LC or LF diet during 6 months. The pre-planned primary trial end-point was the weight loss. Differences between the groups were assessed using one-way ANOVA. There were three women (2·8 %) who dropped out, all of them in the CBT group. No differences in the anthropometric and laboratory characteristics at baseline were noted between women in the CBT (n 52) and control groups (n 50). Intention-to-treat analysis showed that weight loss in the CBT-LC (90 (sd 12·3) to 82·1 (sd 12·1) kg) and C-LC (89·4 (sd 10·0) to 85·8 (sd 9·8) kg) groups reached 8·7 and 4·0 %, respectively (P < 0·0001), and in the CBT-LF (87·9 (sd 11·4) to 79·4 (sd 11·8) kg) and C-LF (88·8 (sd 14·5) to 85·3 (sd 14·3) kg) groups it was 9·7 and 3·9 %, respectively (P < 0·05). Weight loss was higher in the CBT-LF group than in the CBT-LC groups (P = 0·049). The present results showed that adding CBT to either the LF or LC diet produced significantly greater short-term weight loss in obese women compared with diet alone. These finding support the efficacy of CBT in breaking previous dietary patterns and in developing healthier attitudes that reinforce a healthier lifestyle.

Obesity is a chronic disorder caused by an imbalance of the energy metabolism with high associated burdens. Therefore, huge efforts are being currently devoted in studying new types of hypoenergetic diets and their composition, in order to characterise more specific, long-lasting and safe slimming protocols. A number of investigations are trying to determine the specific influence of the macronutrient distribution in energy-restricted diets on the management of excessive body weight. In this context, very-low-energy diets supplying between 1670 and 3350 kJ (400 and 800 kcal)/d have been beneficial in short-term treatments causing a weight loss of 300–500 g/d. Such strategies place more emphasis on energy restriction than on the macronutrient composition of the diet prescription. Weight loss produced by either low-carbohydrate or low-fat moderately energy-restricted diets ranges from 0·5 to 1·0 kg/week, while diets with high or moderately high protein content have also been applied in weight-reducing programmes by inducing losses of 0·2–0·4 kg/week. Other factors that determine weight loss by dieting are sex, age, initial body weight, race, genetics, regional fat deposition, etc, which must be taken into account to explain the variability in the outcomes of different low-energy diets. Therefore, more research is needed about the impact of diets with different fuel substrates and foods on the characteristics of the weight-loss process.

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.