The percentage of US adults following low-carbohydrate diets (LCD) doubled in the last decade. Some researchers observed this trend with concern and highlighted the potential for nutritional deficiencies and impaired overall diet quality with LCD. The present study investigated nutrient intake in a nationally representative sample of 307 US adults following an LCD. Using cross-sectional data from the National Health and Nutrition Examination Surveys, we compared nutrient intake profiles in said individuals with the daily nutritional goals specified in the current 2020–2025 Dietary Guidelines for Americans (DGA). Results were then compared with the general population consuming a standard American diet. Almost 57 % of low-carbohydrate dieters were female, and the mean age was 48·67 (1·35) years. Individuals consuming LCD exceeded the recommendations for saturated fat, total lipid and sodium intake (both sexes). An insufficient intake was observed for fibre, Mg, potassium and several other vitamins (vitamins A, E, D in both sexes as well as vitamin C in men and folate in women). Neither men nor women met the recommendations for fibre intake. A comparable picture was found for the general population. The potentially insufficient intake of several essential nutrients in LCD warrants consideration and a careful assessment with regard to the current DGA.

There are two proven dietary approaches to shift type 2 diabetes (T2D) into remission: low-energy diets (LEDs) and low-carbohydrate diets (LCDs). These approaches differ in their rationale and application yet both involve carbohydrate restriction, either as an explicit goal or as a consequence of reducing overall energy intake. The aims of this systematic review were to identify, characterise and compare existing clinical trials that utilised ‘low-carbohydrate’ interventions with differing energy intakes. Electronic databases CENTRAL, CINAHL, Embase, MEDLINE and Scopus were searched to identify controlled clinical trials in adults with T2D involving low-carbohydrate intake (defined as <130 g carbohydrate/d) and reporting weight and glycaemic outcomes. The initial database search yielded 809 results, of which fifteen studies met the inclusion criteria. Nine out of fifteen studies utilised LCDs with moderate or unrestricted energy intake. Six trials utilised LEDs (<1200 kcal/d), with all except one incorporating meal replacements as part of a commercial weight loss programme. Interventions using both restricted and unrestricted (ad libitum) energy intakes produced clinically significant weight loss and reduction in glycated haemoglobin (HbA1c) at study endpoints. Trials that restricted energy intake were not superior to those that allowed ad libitum low-carbohydrate feeding at 12 and 24 months. An association was observed across studies between average weight loss and reduction in HbA1c at 6, 12 and 24 months, indicating that sustained weight loss is key to T2D remission. Further research is needed to specifically ascertain the weight-independent effects of carbohydrate restriction on glycaemic control in T2D.

Few studies have suggested that long-term adherence to low-carbohydrate diets (LCD) may affect maternal glucose metabolism in Western countries. We aimed to investigate the association between LCD during pregnancy and glucose metabolism in a Chinese population. A total of 1018 women in mid-pregnancy were recruited in 2017–2018. Participants underwent a 75 g oral glucose tolerance test (OGTT). Daily dietary intakes over the past month were accessed using a validated FFQ. The overall, animal and vegetable LCD scores which represent adherence to different low-carbohydrate dietary patterns were calculated. Mixed linear regression and generalised linear mixed regression were conducted to evaluate the associations between LCD scores and maternal glucose metabolism. Of the 1018 subjects, 194 (19·1 %) were diagnosed with gestational diabetes mellitus (GDM). The overall LCD score (β: 0·024, se 0·008, PFDR = 0·02) and animal LCD score (β: 0·023, se 0·008, PFDR = 0·02) were positively associated with OGTT 1-h glucose. No significant associations were found between the three different LCD scores with fasting plasma glucose, OGTT 2-h glucose, or insulin resistance, respectively. Compared with the lowest quartile, the crude OR of GDM for the highest quartile were 1·84 (95 % CI 1·14, 2·95) for overall LCD score (Pfor trend = 0·02) and 1·56 (95 % CI 1·00, 2·45) for animal LCD score (Pfor trend = 0·02). However, these associations became non-significant after adjustment for covariates. In conclusion, a low-carbohydrate dietary pattern with high animal protein and fat is associated with higher postprandial 1-h glucose levels in Chinese pregnant women.

The evidence linking low-carbohydrate diets (LCD) to CVD is controversial, and results from epidemiological studies are inconsistent. We aimed to assess the relationship between LCD patterns and coronary artery Ca (CAC) scores from computed tomography in the Multi-Ethnic Study of Atherosclerosis cohort. Our sample included 5614 men and women free of clinical CVD at baseline (2000–2002), who had a FFQ, a baseline measure and ≥1 measure of CAC during follow-up. We excluded those with implausible energy intake or daily physical activity. The overall, animal-based and plant-based LCD scores were calculated based on intakes of macronutrients. Relative risk regression and robust regression models were used to examine the cross-sectional and longitudinal relationship between LCD score quintile and CAC outcomes, after adjustment for multiple cardiovascular risk factors. The mean age of participants was 63 years. The median intakes of total carbohydrate, fat and protein were 53·7, 30·5 and 15·6 % energy/d, respectively. Among 2892 participants with zero CAC scores at baseline, 264 developed positive scores during 2·4-year follow-up (11–59 months). Among those with positive scores at baseline, the median increase in CAC was 47 units over the course of follow-up. The overall, the animal-based and the plant-based LCD scores were not associated with CAC prevalence, incidence and progression. In conclusion, diets low in carbohydrate and high in fat and/or protein, regardless of the sources of protein and fat, were not associated with higher levels of CAC, a validated predictor of cardiovascular events, in this large multi-ethnic cohort.

We aimed to clarify the effect of low-carbohydrate diet (LCD) on renal function in overweight and obese individuals without chronic kidney disease (CKD). Literature searches were performed using EMBASE, MEDLINE and Cochrane Library until December 2015. We selected articles that reported human studies from their inception until December 2015 in English using the following searching terms: ‘Low carbohydrate diet’ AND (‘Clinical trial’ OR ‘Clinical study’ OR ‘Clinical investigation’ OR ‘Observational study’ OR ‘Cohort study’). We compared the effects of LCD on renal function, defined as change in estimated glomerular filtration rate (eGFR), assessed in randomised-controlled trials. We calculated the mean change in eGFR and the mean change in standard deviations by eGFR or creatinine clearance, and compared the mean change in eGFR and standard deviations in LCD with those in the control diet using fixed-effects models. We selected nine randomised controlled trials including 1687 participants (861 were fed LCD and 826 were fed the control diet). The mean change in eGFR in the LCD group was −4·7 to 24·0 ml/min per 1·73 m2 and that in the control diet group was −4·1 to 10·8 ml/min per 1·73 m2. The mean change in eGFR in the LCD group was greater than that in the control diet (0·13 ml/min per 1·73 m2; 95 % CI 0·00, 0·26). In the present meta-analysis, we identified that the increase in eGFR was greater in LCD compared with the control diet in overweight and obese individuals without CKD.

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.

Long-term safety of consuming low-carbohydrate diets (LCD) in Asian populations, whose carbohydrate intake is relatively high, is not known. In the present study, the association of LCD with CVD and total mortality was assessed using data obtained in the NIPPON DATA80 (National Integrated Project for Prospective Observation of Non-communicable Disease and Its Trends in the Aged 1980) during 29 years of follow-up. At baseline in 1980, data were collected from study participants aged ≥ 30 years from randomly selected areas in Japan. LCD scores were calculated based on the percentage of energy as carbohydrate, fat and protein, estimated by 3 d weighed food records. A total of 9200 participants (56 % women, mean age 51 years) were followed up. During the follow-up, 1171 CVD deaths (52 % in women) and 3443 total deaths (48 % in women) occurred. The multivariable-adjusted hazard ratio (HR) for CVD mortality using the Cox model comparing the highest v. lowest deciles of LCD score was 0·60 (95 % CI 0·38, 0·94; Ptrend= 0·021) for women and 0·78 (95 % CI 0·58, 1·05; Ptrend= 0·079) for women and men combined; the HR for total mortality was 0·74 (95 % CI 0·57, 0·95; Ptrend= 0·029) for women and 0·87 (95 % CI 0·74, 1·02; Ptrend= 0·090) for women and men combined. None of the associations was statistically significant in men. No differential effects of animal-based and plant–fish-based LCD were observed. In conclusions, moderate diets lower in carbohydrate and higher in protein and fat are significantly inversely associated with CVD and total mortality in women.

The role of very-low-carbohydrate ketogenic diets (VLCKD) in the long-term management of obesity is not well established. The present meta-analysis aimed to investigate whether individuals assigned to a VLCKD (i.e. a diet with no more than 50 g carbohydrates/d) achieve better long-term body weight and cardiovascular risk factor management when compared with individuals assigned to a conventional low-fat diet (LFD; i.e. a restricted-energy diet with less than 30 % of energy from fat). Through August 2012, MEDLINE, CENTRAL, ScienceDirect, Scopus, LILACS, SciELO, ClinicalTrials.gov and grey literature databases were searched, using no date or language restrictions, for randomised controlled trials that assigned adults to a VLCKD or a LFD, with 12 months or more of follow-up. The primary outcome was body weight. The secondary outcomes were TAG, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), systolic and diastolic blood pressure, glucose, insulin, HbA1c and C-reactive protein levels. A total of thirteen studies met the inclusion/exclusion criteria. In the overall analysis, five outcomes revealed significant results. Individuals assigned to a VLCKD showed decreased body weight (weighted mean difference − 0·91 (95 % CI − 1·65, − 0·17) kg, 1415 patients), TAG (weighted mean difference − 0·18 (95 % CI − 0·27, − 0·08) mmol/l, 1258 patients) and diastolic blood pressure (weighted mean difference − 1·43 (95 % CI − 2·49, − 0·37) mmHg, 1298 patients) while increased HDL-C (weighted mean difference 0·09 (95 % CI 0·06, 0·12) mmol/l, 1257 patients) and LDL-C (weighted mean difference 0·12 (95 % CI 0·04, 0·2) mmol/l, 1255 patients). Individuals assigned to a VLCKD achieve a greater weight loss than those assigned to a LFD in the long term; hence, a VLCKD may be an alternative tool against obesity.

Intermittent energy restriction may result in greater improvements in insulin sensitivity and weight control than daily energy restriction (DER). We tested two intermittent energy and carbohydrate restriction (IECR) regimens, including one which allowed ad libitum protein and fat (IECR+PF). Overweight women (n 115) aged 20 and 69 years with a family history of breast cancer were randomised to an overall 25 % energy restriction, either as an IECR (2500–2717 kJ/d, < 40 g carbohydrate/d for 2 d/week) or a 25 % DER (approximately 6000 kJ/d for 7 d/week) or an IECR+PF for a 3-month weight-loss period and 1 month of weight maintenance (IECR or IECR+PF for 1 d/week). Insulin resistance reduced with the IECR diets (mean − 0·34 (95 % CI − 0·66, − 0·02) units) and the IECR+PF diet (mean − 0·38 (95 % CI − 0·75, − 0·01) units). Reductions with the IECR diets were significantly greater compared with the DER diet (mean 0·2 (95 % CI − 0·19, 0·66) μU/unit, P= 0·02). Both IECR groups had greater reductions in body fat compared with the DER group (IECR: mean − 3·7 (95 % CI − 2·5, − 4·9) kg, P= 0·007; IECR+PF: mean − 3·7 (95 % CI − 2·8, − 4·7) kg, P= 0·019; DER: mean − 2·0 (95 % CI − 1·0, 3·0) kg). During the weight maintenance phase, 1 d of IECR or IECR+PF per week maintained the reductions in insulin resistance and weight. In the short term, IECR is superior to DER with respect to improved insulin sensitivity and body fat reduction. Longer-term studies into the safety and effectiveness of IECR diets are warranted.

Low-carbohydrate diets have become increasingly popular for weight loss. Although they may improve some metabolic markers, particularly in type 2 diabetes mellitus (T2D) or the metabolic syndrome (MS), their net effect on arterial wall function remains unclear. The objective was to evaluate the relation between dietary macronutrient composition and the small artery reactive hyperaemia index (saRHI), a marker of small artery endothelial function, in a cohort of patients at increased cardiovascular (CV) risk. The present cross-sectional study included 247 patients. Diet was evaluated by a 3-d food-intake register and reduced to a novel low-carbohydrate diet score (LCDS). Physical examination, demographic, biochemical and anthropometry parameters were recorded, and the saRHI was measured in each patient. Individuals in the lowest LCDS quartile (Q1, 45 % carbohydrate; 20 % protein; 32 % fat) had higher saRHI values than those in the top quartile (Q4, 29 % carbohydrate, 24 % protein, 40 % fat; 1·66 (sd 0·41) v. 1·52 (sd 0·22), P= 0·037). These results were particularly strong in patients with the MS (Q1 = 1·82 (sd 0·32) v. Q4 = 1·61 (sd 027); P= 0·021) and T2D (Q1 = 1·78 (sd 0·31) v. Q4 = 1·62 (sd 0·35); P= 0·011). Multivariate analysis demonstrated that individuals in the highest LCDS quartile had a significantly negative coefficient of saRHI, which was independent of confounders (OR − 0·85; 95 % CI 0·19, 0·92; P= 0·031). These findings suggest that a dietary pattern characterised by a low amount of carbohydrate, but high amounts of protein and fat, is associated with a poorer small artery vascular reactivity in patients with increased CV risk.

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.

Very low-carbohydrate diets are often used to promote weight loss, but their effects on bowel health and function are largely unknown. We compared the effects of a very low-carbohydrate, high-fat (LC) diet with a high-carbohydrate, high-fibre, low-fat (HC) diet on indices of bowel health and function. In a parallel study design, ninety-one overweight and obese participants (age 50·6 (sd 7·5) years; BMI 33·7 (sd 4·2) kg/m2) were randomly assigned to either an energy-restricted (about 6–7 MJ, 30 % deficit) planned isoenergetic LC or HC diet for 8 weeks. At baseline and week 8, 24 h urine and faecal collections were obtained and a bowel function questionnaire was completed. Compared with the HC group, there were significant reductions in the LC group for faecal output (21 (sd 145) v. − 61 (sd 147) g), defecation frequency, faecal excretion and concentrations of butyrate ( − 0·5 (sd 10·4) v. − 3·9 (sd 9·7) mmol/l) and total SCFA (1·4 (sd 40·5) v. − 15·8 (sd 43·6) mmol/l) and counts of bifidobacteria (P < 0·05 time × diet interaction, for all). Urinary phenols and p-cresol excretion decreased (P ≤ 0·003 for time) with no difference between diets (P ≥ 0·25). Faecal form, pH, ammonia concentration and numbers of coliforms and Escherichia coli did not change with either diet. No differences between the diets were evident for incidences of adverse gastrointestinal symptoms, which suggests that both diets were well tolerated. Under energy-restricted conditions, a short-term LC diet lowered stool weight and had detrimental effects on the concentration and excretion of faecal SCFA compared with an HC diet. This suggests that the long-term consumption of an LC diet may increase the risk of development of gastrointestinal disorders.

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.

One approach to achieve weight loss and decrease both obesity and associated morbidities involves high-protein, low-carbohydrate (HPLC) diets. This study compares the impact on metabolic health of HPLC and high-protein, medium-carbohydrate (HPMC) diets offered to diet-induced obese (DIO) rats. Weanling male rats were fed either a 37 % fat diet (n 48) or stock pellets (n 12) for 22 weeks. Rats fed the 37 % fat diet accumulated more body fat (26·6 versus 14·8 % body weight, P < 0·001) compared with those on stock diet. The DIO rats had higher systolic blood pressure (+6·6 mmHg, P = 0·002), fasting insulin (+63 % P = 0·006) and areas under the glucose (+21 %, P < 0·001) and insulin (+81 %, P < 0·001) curves following an oral glucose tolerance test. DIO rats were then separated into four groups and offered for 8 weeks either: (1) the 37 % fat diet; (2) an HPLC or (3) HPMC diet; or (4) fed the 37 % fat diet to the intake of the HPMC group. Rats offered the 37 % fat or HPLC diets gained while those on HPMC lost body fat. Blood pressure was not altered by the dietary switch. Both HPLC and HPMC rats had lowered fasting insulin (P = 0·027) and improved homeostatic assessment (HOMA; P = 0·011) that was not different from those of stock animals. These improvements occurred despite differences in fat gain, and indicate that both weight loss and macronutrient intake can impact favourably on obesity-associated morbidities.