Low-Carbohydrate or Low-Fat Diet?

Trials published up to now on the comparison between low-carbohydrate and low-fat diet have considered short-term results, so now, in the USA, the results from a 2-year trial are published, where 307 obese adults (average BMI 36 kg/ m2) have been randomized to a low-carbohydrate diet with no fat restriction or to a low-fat diet (about 30% of calories derived from fats). All participants have received some behavioural instructions, both for weight self-control and for physical exercise. Diabetics and patients with lipid metabolism alterations have been excluded from the trial. With both types of diet, weight loss has been of about 11 kg after one year and of 7 further kg after two years. There has been no difference, in the end, in the levels of triglycerides, of LDL cholesterol, of total cholesterol/HDL cholesterol relation. The levels of HDL cholesterol, instead, resulted higher in the group fed with the low-carbohydrate diet (about 2 mg/dl more). The continuous compliance with the diet has been of about 50% after two years.

Apart from the question whether it is better to reduce carbohydrates or fats to lose weight, the important datum of this trial is that 50% of participants has discontinued diet within 2 years, and this explains very much on the difficulty to lose weight.

Antioxidants and Mortality -

Even if it is a common opinion that dietetic supplements are able to protect against oxidative stresses, trials concerning this subject have never given a convincing demonstration of the real usefulness of these supplements. Now, a meta-analysis has been performed on 68 randomized trials, involving more than 230.000 subjects, of whom about 70% was in good health. Both used doses and the duration of treatments were very variable and the supplements were administered as a single dietetic supplement or as an association of various substances. Analysing the 47 trials with high methodological quality researchers saw that betacarotene, vitamin A and vitamin E, administered singularly or in association with other supplements, have significantly increased the mortality risk (RR 1,05 – 1,16 – 1,04 respectively), while vitamin C and selenium had no effects on the overall mortality.

Even if the increase in the overall mortality risk seen through betacarotene, vitamin A and vitamin E supplements is little, however the use of these substances should be not advised in primary or secondary prevention. Obviously, the results of these trials refer to chemical supplements of single substances, and they cannot be adapted to food (fruit and vegetables) consumption, rich in the same substances.

About Diets

For body weight loss in general a low-calorie, low-lipid, normal-carbohydrate diet is recommended, even if some nutritionists instead advise a low-carbohydrate diet. A randomized study was then performed, taking into consideration four popular diets: Atkins (strongly low-carbohydrate diet), Zone (low-carbohydrate diet), LEARN (normal-carbohydrate low-lipid diet), Ornish (strongly low-lipid and strongly hyper-carbohydrate diet). Participants were 311 obese, non-diabetic, pre-menopausal women (age range between 25 and 50; 71% of white race; average BMI 32). The compliance with diets after a year resulted similar in all the four groups (76%-88%). After a year, weight loss was higher with Atkins diet (-4,7 kg), followed by Ornish diet (-2,6 kg), by LEARN diet (-2,2 kg) and in the end by Zone diet (-1,6 kg). Only the difference between Atkins and Zone diets was statistically significant. After a year, the Atkins diet gave the greatest increase in HDL cholesterol (averagely 5 mg/dl vs. less than 3 mg/dl with the other three diets), the greatest decrease in triglycerides (29 mg/dl vs. less than 15 mg/dl) and of OSAP (7,6 mmHg vs. less than 4 mmHg for systolic pressure; 4,4 mmHg vs. less than 3 mmHg for diastolic pressure). With Ornish diet it was seen the greatest decrease of LDL cholesterol (4 mg/dl vs. less than 1 mg/dl with other diets). The slight modifications in insulinemia and glycaemia were practically identical in the four groups.

The analysis was exact and, according to these data, a strongly low-carbohydrate diet like the Atkins diet gives the best results as to weight loss and decrease in cardiovascular risk factors, even if the advantage compared to other diets is not significant. It would be also necessary to examine other subgroups of patients (diabetics, people with hypertension, males), before affirming which is the best diet.

Eating Quickly and Eating Until Full -

The fast introduction of food is associated with an increased intake of energy, with an increase in weight and with overweight (BMI ≥ 25): in this Japanese trial, 3287 adults (between 30 and 69) have been examined as to eating quickness and the habit to eat until full, in order to verify whether one of these two aspects, or their combination, more easily leads to overweight. In the overall, 46% of males and 36% of females referred to eat quickly, while 51% of males and 58% of females told to eat until full (that is to say to eat a great amount of food within a single meal). After the various adjustments (age, gender, smoke habit, physical exercise, job, total energetic intake, fiber intake, alcohol consumption, geographical area of origin), the quickness of food intake was significantly associated with overweight (OR about 2.0 for both genders), and researchers arrived at the same conclusion examining the aspect of eating until full. Subjects referring to eat quickly and to eat until full presented an OR of about 3.0 as to overweight easiness compared with the subjects eating slowly and not until full.

The trial is small and presents some faults: first of all, data were collected according to a declaration and not to observation; secondly, a causal connection between these two food habits and overweight cannot be shown. In order to obtain reliable results, it is necessary to perform prospective trials and to verify whether the change in these habits implies a BMI decrease. In any case, to lose some more minutes at the table and avoiding to eat until full are good-sense advices which everyone should put into practice, independently from Japanese trials.