Preface
Food restriction therapy is a method of preventing or treating a disease by limiting daily caloric intake while ensuring basic nutritional requirements. Although food restriction therapy has been widely used for metabolic diseases such as type 2 diabetes, fatty liver, and aging-related diseases such as cardiovascular and neurodegenerative diseases, the earliest and most widespread application of this method is for weight reduction in patients with obesity.
The role of food restriction therapy in weight reduction is undisputed, but the relationship between food restriction and weight control has been discussed by scholars without interruption. The main concerns include the magnitude of weight loss caused by food restriction, the rebound problem, factors affecting weight loss and rebound, and the safety of food restriction in children and the elderly.
Weight loss effect of food restriction therapy and its benefits
1. Weight loss effect of food restriction therapy
Food restriction therapy programs vary, and the effect of weight loss is not the same for different food restriction programs. For obesity, type 2 diabetes and other metabolic diseases, the most used intervention method is to reduce daily caloric intake by 15% to 40%, that is, the caloric intake of about 1200 to 1800 kcal/d, long-term maintenance; there are also some studies using 800 kcal/d or even lower very low calorie diet, short-term intervention, in order to achieve rapid weight loss. Early researchers used the method of absolute fasting to treat obese patients, and found that for the first 10 d, the average daily weight loss was 800~900 g, of which, 50%~70% was water; by 30 d of fasting, the weight loss was halved compared to the previous, the negative balance of water metabolism was corrected, the basal metabolic rate was reduced, and energy expenditure and activity were reduced; about 5 kg of muscle tissue was lost after 1 month of fasting, and after 2 months Approximately 2, 8 kg of muscle tissue is lost. However, absolute fasting is no longer used clinically because it can lead to serious adverse effects or even death.
Lifestyle interventions for pre-diabetic or obese patients generally require a weight loss of about 7%. The above studies confirm that most patients who implement standard caloric restriction can achieve their weight loss goals within six months, and that more stringent caloric restriction can lead to further weight loss.
In lifestyle interventions where exercise and dietary control go hand in hand, are they consistent in their weight loss effects? The American scholar Hall used a computer to simulate the weight loss effects of diet or exercise alone based on changes in energy expenditure, body weight and fat content, and found that diet alone lost 34 kg in 30 weeks, of which 65% came from fat loss, while exercise alone lost 27 kg in 30 weeks, 102% from fat loss. Although the weight loss was more significant with diet alone, about 35% of the weight loss was from defatted weight; in contrast, exercise primarily reduced body fat content, with a mild increase in defatted weight (lean tissue). Therefore, researchers recommend that 20% caloric restriction combined with 20 min/d of exercise is the most appropriate long-term strategy for weight control.
2, the weight loss benefit of food restriction therapy
Food restriction therapy was first used to treat obesity in order to reduce the risk of a range of diseases caused by obesity through weight loss. Subsequently, it was found that for obese or overweight type 2 diabetes patients, weight loss caused by food restriction can bring many benefits to patients, such as improving glucose metabolism rate, reducing fasting blood sugar and fasting insulin level, increasing insulin sensitivity, reducing blood pressure, reducing triglyceride level, increasing high-density lipoprotein cholesterol (HDL-C) content; improving sleep apnea syndrome in obese patients, improving sleep apnea syndrome in obese patients, and improving sleep apnea syndrome in obese patients. Improving the fertility of patients, especially in women with polycystic ovary syndrome. Retrospective studies have shown that for every 1 kg of weight loss in type 2 diabetes, life expectancy increases by 3 to 4 months.
The American Action for Health in Diabetes (Look AHEAD) study was designed to see if weight loss from an intensive biochemical modality intervention could reduce cardiovascular morbidity and mortality in overweight/obese patients with type 2 diabetes. Recently, the group published the results: at a mean follow-up of 9,6 years, the intensive lifestyle intervention group had more significant weight loss, more significant reductions in glycated hemoglobin and more significant improvements in all cardiovascular risk factors except LDL cholesterol compared to the health education group, but there was no difference in the incidence of cardiovascular events between the two groups. Although the study did not show that intensive lifestyle weight loss reduced cardiovascular events, the investigators still believe that lifestyle interventions for weight loss are a cornerstone of diabetes treatment and that there is still a strong case for encouraging patients to lose weight, and predict that differences in mortality between the two groups will be observed after several years.
Factors influencing weight loss and rebound
1. Factors affecting weight loss
The effects and benefits of weight loss after food restriction were not the same in men and women. Wong et al. found that the magnitude of weight loss after food restriction was significantly greater in men than in women, and that in addition to fat content and fasting glucose levels, the improvement in body mass index, fasting insulin, insulin resistance index (HOMA-IR), HDL-C, and triglycerides were better in men than in women. In addition to Wong et al.’s study, several clinical studies have also found that weight loss was significantly greater in men than in women after food restriction, which may be related to different body composition ratios, sex hormone levels, and appetite control in men and women.
Chaput et al. reported that sleep quality and sleep duration also affected weight loss, with poor sleep quality and short sleep duration reducing leptin secretion and increasing ghrelin secretion. In addition, the amount of water consumed during food restriction also affects the weight loss effect, and the study confirmed that the weight loss of the former group was more obvious when compared with the non-drinking group.
2. Factors affecting weight regain
The purpose of weight loss through food restriction is easy to obtain, however, to maintain this weight control achievement is much more difficult. One of the major problems faced by most people who have lost weight is the rebound of weight after resuming the diet. The Look AHEAD study found that after 4 years of lifestyle interventions such as food restriction and exercise, nearly half of the patients maintained a weight loss of >5%; those who maintained their weight loss generally continued to control their weight with a low-calorie diet, exercised consistently, visited their doctor frequently, and communicated with their doctor compared to those who regained weight. A strong subjective intention to lose weight resulted in a lower incidence of rebound.
In addition to subjective intention, are there any objective indicators that can predict rebound, Wong et al. found that among those who regained weight, the changes in body mass index, fasting insulin and HOMA-IR were inversely correlated with rebound after early dieting, i.e., the more significant the reduction in body mass index, the more significant the decrease in fasting insulin and the more significant the improvement in insulin resistance, the smaller the rebound. The more the body mass index is reduced, the more the fasting insulin is reduced and the more the insulin resistance is improved, the less the weight regain; and insulin sensitivity can be used to predict the risk of weight regain independently of body mass index.
Boule et al. reported that weight regain was more pronounced in those with lower glucose values at 2h after oral glucose tolerance test (OGTT); a study from India also showed that the more pronounced glucose increase after OGTT glucose load, the less weight gain.
It is now believed that rebound is not only associated with changes in some anthropometric and biochemical indicators during weight loss, but also with different responses of genes regulating fatty acid metabolism, tricarboxylic acid cycle, oxidative phosphorylation, apoptosis and other pathways in patients during the process of food restriction. However, relatively few studies have explored the molecular mechanisms of weight rebound compared to the simple and readily available anthropometric indicators.
Food restriction and weight loss in special populations
The weight loss effects and health benefits of food restriction therapy are clear, and under medical supervision, most patients can safely and effectively undergo food restriction therapy. However, for elderly obese patients, there are some controversies about the safety of weight control through food restriction.
1. Food restriction and weight reduction in elderly obese patients
Obese elderly people (age ≥ 65 years old, body mass index ≥ 30kg/m2) is increasing year by year, in 2010 the United States obese elderly population rose to 37, 45%. The health status of obese patients is much worse than that of non-obese people of the same age, especially the risk of cardiovascular disease is significantly increased. By reducing weight, obese elderly patients can also reduce body fat, increase physical fitness, and improve metabolic and cardiovascular risk indicators; however, weight loss in the elderly has safety issues that cannot be ignored: while reducing body fat content, there is a risk of loss of defatted weight (lean tissue) and decreased bone density. Therefore, despite the many benefits of food restriction for weight loss, geriatricians still try to avoid weight loss interventions when dealing with obese patients in old age.
In 2013, Waters et al. conducted a systematic review of weight loss in obese elderly patients, in which the paper focused on whether weight loss in obese elderly patients can be achieved through food restriction, whether weight loss in elderly patients is safe, and whether the effectiveness of weight loss can be maintained. It is concluded that in obese elderly patients aged 65 years and older who are physically inactive, a 10% weight loss can be achieved through diet control or exercise, and that this weight loss and the improvement in body fat, physical fitness, and insulin sensitivity brought about by weight loss can be maintained over a long period of time (maximum follow-up of 30 months); while losing weight, patients also have a decrease in bone mineral density and desaturation weight, and exercise and calcium and vitamin D supplementation can alleviate bone mineral density and desaturation weight. The loss of bone mineral density and body weight can be mitigated, but not completely prevented, by exercise and calcium and vitamin D supplementation. Therefore, the loss of BMD and dead weight is still the primary reason for the controversy of weight loss in elderly obese patients. However, because of the generally high baseline BMD in older obese patients and the fact that weight loss improves fitness and metabolism-related indicators, the clinical significance of the adverse effects remains inconclusive. The previous view that obesity is osteoprotective is being challenged with new findings suggesting that excess adipose tissue has a damaging effect on bone. However, restrictive diets, despite leading to a decrease in bone mass, can improve bone quality by reducing the inflammatory response. Further, it is unclear whether the improvement in physical performance from weight loss can balance or even reverse the effects of decreased bone mineral density and reduce the overall risk of falls and fractures in older patients. Therefore, risk studies between weight loss and bone loss still need to be validated by rigorous clinical trials with a non-weight loss control group to exclude the confounding role of aging in bone loss.
In conclusion, the pros and cons of food restriction and weight loss in the obese aging population are still inconclusive. There is an urgent need for a large sample of long-term follow-up trials to assess the effect of weight loss and long-term prognosis of this population, as well as further studies to explore the molecular mechanisms of muscle and bone loss in weight loss in elderly obese patients.
2.Children obesity patient’s food restriction and weight reduction
Childhood obesity has become a global public health problem, the treatment of obese children also focus on weight control. In view of the special period of growth and development of children and adolescents, food restriction must first ensure energy supply. Recent studies have concluded that a low-carbohydrate ketogenic diet (<20-50g/d) is more appropriate for children with obesity. Although both ketogenic diet and low-fat diet can effectively reduce patients' body weight, the former has better improvement on metabolic indicators such as body weight, blood lipids and insulin sensitivity; moreover, low-carbohydrate diet can cause chronic mild ketosis in the body, and ketone bodies act on the central nervous system, causing increased satiety and reduced food intake, resulting in increased compliance with food restriction in children. However, there are few studies on the treatment of childhood obesity, and the safety and efficacy of food restriction treatment need more evidence-based medical evidence.
Summary
In conclusion, food restriction has a significant effect on weight reduction and can reduce the risk of cardiovascular diseases such as hyperlipidemia, hypertension, hyperglycemia, and hyperinsulinemia associated with obesity. Clinically, the importance and necessity of food restriction for weight reduction should be emphasized in patients with obesity, type 2 diabetes and other metabolic diseases. For obese elderly patients, food restriction can be carried out under the guidance of a physician after weighing the pros and cons and assessing the risks, taking into account the patient’s own health condition.