Low-fat versus low-carbohydrate weight reduction diets: effects on weight loss, insulin resistance, and cardiovascular risk: a randomized control trial

Quantification of the effect of energy imbalance on bodyweight

Obesity interventions can result in weight loss, but accurate prediction of the bodyweight time course requires properly accounting for dynamic energy imbalances. In this report, we describe a mathematical modelling approach to adult human metabolism that simulates energy expenditure adaptations during weight loss. We also present a web-based simulator for prediction of weight change dynamics. We show that the bodyweight response to a change of energy intake is slow, with half times of about 1 year. Furthermore, adults with greater adiposity have a larger expected weight loss for the same change of energy intake, and to reach their steady-state weight will take longer than it would for those with less initial body fat. Using a population-averaged model, we calculated the energy-balance dynamics corresponding to the development of the US adult obesity epidemic. A small persistent average daily energy imbalance gap between intake and expenditure of about 30 kJ per day underlies the observed average weight gain. However, energy intake must have risen to keep pace with increased expenditure associated with increased weight. The average increase of energy intake needed to sustain the increased weight (the maintenance energy gap) has amounted to about 0·9 MJ per day and quantifies the public health challenge to reverse the obesity epidemic.

The assessment of vascular function during dietary intervention trials in human subjects

The potential to reduce cardiovascular morbidity through dietary modification remains an area of intense clinical and scientific interest. Any putatively beneficial intervention should be tested within a randomised controlled trial which records appropriate endpoints, ideally incident CVD and death. However, the large sample sizes required for these endpoints and associated high costs mean that the majority of dietary intervention research is conducted over short periods among either healthy volunteers or those at only slightly increased risk, with investigators using a diverse range of surrogate measures to estimate arterial health in these studies. The present review identifies commonly employed techniques, discusses the relative merits of each and highlights emerging approaches.

Nutrition therapy and the management of obesity and diabetes: an update

Diabetes and obesity have each become a national health crisis in recent years. The number of people who have diabetes and prediabetes continues to grow with a predicted number of 336 million people worldwide with type 2 diabetes by 2030. The prevalence of diabetes has risen in parallel with the increased prevalence of obesity. The optimal nutrition therapy for the treatment of both diabetes and obesity remains controversial. Health care practitioners are no longer solely prescribing the conventional low-fat, higher-carbohydrate diet approach that was used for over a decade. Lower-carbohydrate, higher-fat, or higher-protein diets are now being viewed as equally or sometimes more effective treatment plans for diabetes and obesity. In addition, there are other aspects of diet beyond macronutrient composition that are currently being investigated. This article will summarize research conducted over the past 2 years examining medical nutrition therapy for diabetes and obesity. It will also describe the unique challenges that come with treating this patient population.

Arterial stiffness and wave reflections in marathon runners

BACKGROUND

Regular aerobic exercise has beneficial effects on the cardiovascular system. Marathon running is an aerobic and extremely vigorous exercise. Arterial stiffness and wave reflections are independent predictors of cardiovascular risk. We investigated the acute effect of marathon race on aortic stiffness and wave reflections, as well as possible chronic alterations of these indexes in marathon runners.

METHODS

We studied 49 marathon runners (age 38 +/- 9 years) and 46 recreationally active control subjects (age 37 +/- 5 years). To investigate the acute effect of marathon race, a subgroup of 20 runners was evaluated after the race as well. Aortic stiffness was evaluated with carotid-femoral pulse wave velocity (PWV) and wave reflections with augmentation index (AIx).

RESULTS

Marathon runners had significantly higher systolic, diastolic, pulse (both aortic and brachial), and mean pressures compared to controls (P < 0.05 for all). Marathon runners had significantly higher PWV (6.89 m/s vs. 6.33 m/s, P < 0.01), whereas there was no difference in AIx and AIx corrected for heart rate (AIx@75) compared to controls (13.8% vs. 13.9%, P = 0.985 and 8.2% vs. 10.3%, P = 0.340, respectively). Marathon race caused a significant fall in both AIx (12.2% vs. -5.8%, P < 0.001) and AIx@75 (7.0% vs. 0.0%, P = 0.01), whereas PWV did not change significantly (6.66 m/s vs. 6.74 m/s, P = 0.690). Aortic and brachial systolic, diastolic, and mean pressures were also decreased (P < 0.05).

CONCLUSIONS

A significant fall in wave reflections was observed after marathon race, whereas aortic stiffness was not altered. Moreover, marathon runners have increased aortic stiffness and pressures, whereas wave reflections indexes do not differ compared to controls.