The effects of various sources of dietary fibre on cholesterol metabolism and colonic function in healthy subjects

This thesis deals with the influence of several types of dietary fibre on cholesterol metabolism and colonic function in young healthy subjects. Dietary fibre has been defined as those plant polysaccharides (cellulose, hemicelluloses, pectic substances) and lignin which are resistant to hydrolysis by the digestive enzymes of man.After a general introduction in Chapter 1, a review of reported experiments with healthy subjects is presented in Chapter 2. The few available data on dietary fibre consumption in Western communities are also summarized, and possible mechanisms for the action of dietary fibre on cholesterol metabolism and colonic function are discussed.Chapter 3 describes an experiment with 46 young healthy volunteers. The effects of a mixed high-fibre diet were studied, in which half of the dietary fibre was provided by vegetables and fruits, and the rest cam from cereal products. In Chapter 4 the results are presented from a trial with 62 subjects. In this study the effects of isolated citrus pectin were compared with those of the same amount of pectic substances contained naturally in fruits and vegetables, and also with those of a comparable amount of dietary fibre from wheat bran.Subjects in both studies were under strict dietary control. All foodstuffs except for 200 or 100 kcal (0.8 or 0.4 MJ respectively) per day were individually supplied, taking into account each subject's energy needs. Measurements were made of body weight, food consumption, serum total and high-density lipoprotein (HDL)-cholesterol, faecal mass, the content of steroids, fat, and electrolytes in faeces, frequency of defaecation, intestinal transit-time, and blood pressure.From these two studies it is concluded that in short-term controlled experiments fibre-rich foodstuffs have only a small (vegetables and fruits) or no (bran) favourable effect on the concentration of serum cholesterol. However, in uncontrolled circumstances, a mixed high-fibre diet may through its low fat and cholesterol content indirectly reduce the level of serum cholesterol.After 5 weeks of high-fibre diets the amount and type of dietary fibre had no significant effect on the concentration of serum HDL-cholesterol. The effects on serum total cholesterol could be explained only to a small extent by changes in the excretion of faecal steroids.Although there was a wide interindividual variation in colonic response to increased dietary fibre intake (Chapter 3.2.), in general a high-fibre diet with vegetables and fruits as well as a diet with bran shortened the intestinal transit-time and enhanced faeces production. Thus, it appears that the effects of certain types of dietary fibre on serum cholesterol are unrelated to their effects on colonic function.Finally, the above results are discussed in Chapter 5. It is concluded that a diet rich in cereals, as well as fruits, vegetables, and legumes may be advisable. However, at the present state of knowledge, it would be premature to make precise recommendations for dietary fibre intake

A standardised approach towards PROving the efficacy of foods and Food Constituents for Health CLAIMs (PROCLAIM: providing guidance

Diet is well known to have beneficial health properties that extend beyond traditionally accepted nutritional effects. The approach involved in elucidating these beneficial physiological effects is becoming more important, as reflected by increasing research being undertaken. With growing consumer awareness of foods and food constituents and their relationship to health, the key questions for regulators, scientists and the food industry continue to relate to: (1) how consumers could be protected and have confidence that the health claims on foods are well supported by the evidence; (2) how research on physiological effects of food (constituents) and their health benefits could be stimulated and supported; (3) how research findings could be used in the development of innovative new food products. The objectives of this paper are to provide a set of recommendations on the substantiation of health claims for foods, to develop further guidance on the choice of validated markers (or marker patterns) and what effects are considered to be beneficial to the health of the general public (or specific target groups). Finally, the case for developing a standardised approach for assessing the totality of the available scientific data and weighing the evidence is propose

Overcoming challenges in designing and implementing a phase II randomized controlled trial using a presurgical model to test a dietary intervention in prostate cancer

BackgroundThe time between the diagnosis of cancer and a planned definitive surgical procedure offers a strong and direct approach for assessing the impact of interventions (including lifestyle interventions) on the biology of the target tissue and the tumor. Despite the many strengths of presurgical models, there are practical issues and challenges that arise when using this approach.Purpose/MethodsWe recently completed an NIH-funded phase II trial that utilized a presurgical model in testing the comparative effects of flaxseed supplementation and/or dietary fat restriction on the biology and biomarkers associated with prostatic carcinoma. Herein, we report the rationale for our original design, discuss modifications in strategy, and relay experiences in implementing this trial related to the following topics: (1) subject accrual; (2) subject retention; (3) intervention delivery; and (4) retrieval and completion rates regarding the collection of paraffin-embedded and fresh frozen prostate tissue, blood, urine, ejaculate, anthropometric measures and survey data.ResultsThis trial achieved its accrual target, i.e., a racially-representative (70% white, 30% minority) sample of 161 participants, low rates of attrition (7%); and collection rates that exceeded 90% for almost all biospecimens and survey data. While the experience gained from pilot studies was invaluable in designing this trial, the complexity introduced by the collection of several biospecimens, inclusion of a team of pathologists (to provide validated readings), and shifts in practice patterns related to prostatectomy, made it necessary to revise our protocol; lessons from our experiences are offered within this article.ConclusionsWhile our experience specifically relates to the implementation of a presurgical model-based trial in prostate cancer aimed at testing flaxseed-supplemented and fat-restricted diets, many of the lessons learned have broad application to trials that utilize a presurgical model or dietary modification within various cancer populations