Cassandra E. Forsythe

Diet and exercise for weight loss: a review of current issues.

AbstractObesity is a fast growing epidemic that is primarily due to environmental influences. Nutrition and exercise represent modifiable factors with a major impact on energy balance. Despite considerable research, there remains continued debate regarding the energy content and the optimal macronutrient distribution for promoting healthy and effective weight loss. Low-fat diets have been advised for many years to reduce obesity. However, their effectiveness has been recently challenged, partly because the prevalence of obesity continues to rise despite reductions in fat intake. There are also concerns regarding the methodology of clinical trials showing benefits of fat reduction on weight loss. Although often viewed as a fad diet, very low-carbohydrate (ketogenic) diets are very popular and several recent clinical trials indicate they are more effective at promoting short-term weight loss and improving characteristics of the metabolic syndrome than low-fat diets. However, there is a need to obtain long-term safety and efficacy data. Clearly, weight loss can be achieved with a variety of diet interventions but the effects on other health-related aspects also need to be considered and studied in more detail. Exercise can have positive effects on weight loss, weight control and overall general health, although debate exists concerning the most effective mode, duration and intensity of exercise required to achieve these effects. Importantly, any effective weight control treatment must consider a life-long plan or there will likely be weight regain. Perhaps the most challenging, but rewarding, question that faces researchers is how to predict individual responses to diet and exercise interventions.

Effects of dietary carbohydrate restriction versus low-fat diet on flow-mediated dilation

We previously reported that a carbohydrate-restricted diet (CRD) ameliorated many of the traditional markers associated with metabolic syndrome and cardiovascular risk compared with a low-fat diet (LFD). There remains concern how CRD affects vascular function because acute meals high in fat have been shown to impair endothelial function. Here, we extend our work and address these concerns by measuring fasting and postprandial vascular function in 40 overweight men and women with moderate hypertriacylglycerolemia who were randomly assigned to consume hypocaloric diets (approximately 1500 kcal) restricted in carbohydrate (percentage of carbohydrate-fat-protein = 12:59:28) or LFD (56:24:20). Flow-mediated dilation of the brachial artery was assessed before and after ingestion of a high-fat meal (908 kcal, 84% fat) at baseline and after 12 weeks. Compared with the LFD, the CRD resulted in a greater decrease in postprandial triacylglycerol (-47% vs -15%, P = .007), insulin (-51% vs -6%, P = .009), and lymphocyte (-12% vs -1%, P = .050) responses. Postprandial fatty acids were significantly increased by the CRD compared with the LFD (P = .033). Serum interleukin-6 increased significantly over the postprandial period; and the response was augmented in the CRD (46%) compared with the LFD (-13%) group (P = .038). After 12 weeks, peak flow-mediated dilation at 3 hours increased from 5.1% to 6.5% in the CRD group and decreased from 7.9% to 5.2% in the LFD group (P = .004). These findings show that a 12-week low-carbohydrate diet improves postprandial vascular function more than a LFD in individuals with atherogenic dyslipidemia.

Physiogenomic analysis of weight loss induced by dietary carbohydrate restriction

BackgroundDiets that restrict carbohydrate (CHO) have proven to be a successful dietary treatment of obesity for many people, but the degree of weight loss varies across individuals. The extent to which genetic factors associate with the magnitude of weight loss induced by CHO restriction is unknown. We examined associations among polymorphisms in candidate genes and weight loss in order to understand the physiological factors influencing body weight responses to CHO restriction.MethodsWe screened for genetic associations with weight loss in 86 healthy adults who were instructed to restrict CHO to a level that induced a small level of ketosis (CHO ~10% of total energy). A total of 27 single nucleotide polymorphisms (SNPs) were selected from 15 candidate genes involved in fat digestion/metabolism, intracellular glucose metabolism, lipoprotein remodeling, and appetite regulation. Multiple linear regression was used to rank the SNPs according to probability of association, and the most significant associations were analyzed in greater detail.ResultsMean weight loss was 6.4 kg. SNPs in the gastric lipase (LIPF), hepatic glycogen synthase (GYS2), cholesteryl ester transfer protein (CETP) and galanin (GAL) genes were significantly associated with weight loss.ConclusionA strong association between weight loss induced by dietary CHO restriction and variability in genes regulating fat digestion, hepatic glucose metabolism, intravascular lipoprotein remodeling, and appetite were detected. These discoveries could provide clues to important physiologic adaptations underlying the body mass response to CHO restriction.

Nutritional Aspects of Women Strength Athletes

Strength training elicits sports related and health benefits for both men and women. Although sexual dimorphism is observed in exercise metabolism, there is little information outlining the specific nutritional needs of women strength athletes. Many women athletes restrict energy intake, specifically fat consumption, in order to modify body composition, but this nutritional practice is often counter-productive. Compared to men, women appear to be less reliant on glycogen during exercise and less responsive to carbohydrate mediated glycogen synthesis during recovery. Female strength athletes may require more protein than their sedentary and endurance training counterparts to attain positive nitrogen balance and promote protein synthesis. Therefore, women strength athletes should put less emphasis on a very high carbohydrate intake and more emphasis on quality protein and fat consumption in the context of energy balance to enhance adaptations to training and improve general health. Attention to timing of nutrient ingestion, macronutrient quality, and dietary supplementation (for example, creatine) are briefly discussed as important components of a nutritionally adequate and effective strength training diet for women.

Low-carbohydrate Diets Promote a More Favorable Body Composition Than Low-fat Diets

A PRIMARY CONCERN WITH CONVENTIONAL WEIGHT LOSS APPROACHES IS THE LOSS OF LEAN BODY MASS THAT OCCURS WHEN FAT MASS IS DECREASED. CONSUMING MODERATE PROTEIN, WHILE RESTRICTING CARBOHYDRATE, ALLOWS FOR GREATER PRESERVATION OF LEAN BODY MASS. A LOW-CARBOHYDRATE DIET IN CONJUNCTION WITH PERIODIZED RESISTANCE TRAINING PROMOTES GREATER FAT LOSS WHILE PRESERVING LEAN BODY MASS AND PROMOTING ROBUST IMPROVEMENTS IN METABOLIC HEALTH.

Overview of Creatine Metabolism

Creatine (Cr) was first discovered as an organic constituent of meat some time in the early 1800s. Later in the 1800s, Cr was consistently detected in muscle tissue extracted from various mammals. It was noted that foxes killed in a hunt immediately after running, contained significantly more Cr than normal, providing the first indication that muscular contraction results in an accumulation of Cr. Around the same time, a substance called creatinine (Crn) was detected in the urine and later determined to be a breakdown product of Cr. Phosphocreatine (PCr) was first isolated from muscle tissue in 1927 and found to play an important role in the transfer of energy. Around the same time, two researchers who consumed large quantities of Cr noted that a percentage of the Cr ingested could not be accounted for by excretion in the urine (1). This study was one of the first to indicate that “Cr loading” in muscle is possible when large amounts of Cr are consumed. A great deal of research has been done since this early work to further define the importance of Cr in humans, and the impact of Cr supplementation. In this chapter, the basic metabolism and function of Cr in humans will be overviewed. To what extent and what factors influence blood- and muscle-Cr levels in response to Cr supplementation will be discussed. Also some of the proposed mechanisms that account for the ergogenic effects from Cr usage observed in many studies will be explored.

Diet, exercise and hormone interactions on skeletal muscle

The provision of dietary nutrients is a powerful method by which to alter plasma substrate and hormone concentrations, and to impact cell signalling and protein balance positively in skeletal muscle. Growth hormone, insulin-like growth factor I, testosterone, cortisol and insulin are each uniquely affected by dietary nutrients and exercise. This article summarizes some of the work that has been conducted to assess how diet affects these hormones, in particular the exercise-induced hormone response, with an emphasis on skeletal muscle as a target tissue. Clearly, certain combinations of nutrients, such as carbohydrate combined with protein, can be used to alter nutrient and hormone availability to augment skeletal muscle protein balance. There is a need to link acute diet-induced hormonal responses with chronic muscle adaptations to training, and to determine how chronic manipulations in diet affect training adaptations specific to skeletal muscle.