How does dieting affect your metabolism

A high metabolism means you'll need to take in more calories to maintain your weight. That's one reason why some people can eat more than others without gaining weight. A person with a "low" or slow metabolism will burn fewer calories at rest and during activity and therefore has to eat less to avoid becoming overweight. Lean people tend to be more active during everyday activities than people who are overweight. They may "fidget" more — that is, they tend to be in motion even when engaged in non-exercise activities.

Whether this tendency to move more or less is genetically programmed or learned remains uncertain. But it can add or subtract hundreds of calories each day. Obese people expend more calories, on average, than lean people during most activities, in part because it takes more effort to move around. But they tend to be more sedentary, which makes it harder to get rid of body fat. It's part truth and part myth that metabolism is the key to weight.

The rising tide of obesity in this country cannot be blamed entirely on an inherited tendency to have a slow metabolism. Genes do not change that quickly. Something environmental — particularly, changes in diet and exercising too little — are much more likely culprits. Measurements were taken at baseline, 6 weeks and 12 weeks in the same phase of each woman's menstrual cycle. RMR was determined by indirect calorimetry after a hour fast.

Body composition was measured using standard hydrodensitometry procedures and calculations. Subjects in all three diet groups attended a weekly nutrition class on weight loss. Subjects kept diet records that were evaluated each week. Corrections were made to facilitate a gradual and consistent weight loss of approximately one to two pounds per week. The nutrition intervention included use of a high-fibre, high-carbohydrate supplement.

Based on participants' food records, there were no significant differences in nutrient intake among the three diet groups.

Duration and intensity were progressively increased. Subjects in the aerobic plus resistance training group also completed 11 exercises following heavy resistance training principles three times per week. The control group showed no change in body composition over the week period. All three intervention groups had a significant decline in body mass at 6 weeks, and again at 12 weeks for an average total weight loss of 6.

By 12 weeks there were also significant decreases in percentage body fat: 5. However, there were no significant differences between groups. There were no significant changes in fat-free mass in any of the groups at any time period. There were also no significant changes in resting metabolic rate measured in absolute terms or relative to body mass within groups over time or between groups over time.

Linear regression models between resting metabolic rate and fat-free mass were also tested. The findings regarding no loss of fat-free mass in the diet-only group are surprising, as some degree of obligatory loss of fat-free mass is expected with significant weight loss. The authors state that the high-fibre nature of the participants' diets may have decreased the insulin response to the participants' meals and facilitated lipolytic pathways, thereby sparing fat-free mass from breakdown and oxidation.

The calorie level may be of greater importance in explaining retention of fat-free mass. Much of the work regarding changes in fat-free mass and resting metabolic rate in response to hypocaloric diets have implemented diets containing — kilocalories per day. Such low calorie diets result in a severe calorie deficit and the need to oxidize protein. Information regarding the participants' dietary intake in this study is scant. Only mean intakes per group for the entire week period are presented.

These intakes are approximately — kilocalories less than mean baseline resting metabolic rates. In addition, dietary information is based on self-report, and there is a strong likelihood of underreporting of food intake in obese people.

These relatively small calorie deficits may have enabled subjects to spare protein from oxidation. This rather limited attention and control of dietary intake in general in this area of research is a likely factor contributing to the inconsistency in reported results. Not only is the degree of calorie deficit important, but the distribution of macronutrients and amount of protein per kilogram body weight or fat-free mass is also of great importance in determining fuel substrate utilization.

The calorie deficit, macronutrient distribution and rate of weight loss may be key factors in the retention of fat-free mass and resting metabolic rate. Dietary information should be prescribed and described on an individual basis, i. Although there may have been enough carbohydrate calories to spare protein from oxidation, there may have been insufficient total grammes of protein per kilogram body mass to facilitate an increase in fat-free mass, despite the appropriate stimulus in the resistance training group.

Since all subjects were able to retain fat-free mass, it follows that their resting metabolic rates would also be stable. Decrease in fat oxidation following a meal in weight-reduced individuals: a possible mechanism for weight recidivism. Metabolism ; 45 2 : — Contrasting effects of resistance and aerobic training on body composition and metabolism after diet-induced weight loss.

This two-part study is based on the assumption that a decrease in calorie intake and weight loss is associated with a decrease in resting metabolic rate and fat oxidation. All testing was done while subjects resided at a university clinical research centre. In the first study, 20 older subjects aged 56—70 years underwent an week weight-loss program. Subjects kept food diaries which were reviewed by a registered dietitian at weekly meetings.

During the twelfth week, subjects were requested to increase their intake to allow for weight maintenance and stabilization of weight for post-diet measurements. In the second study, 18 of the 20 weight-reduced subjects began a week exercise regimen, consisting of either aerobic training or weight training.

All subjects attended supervised exercise sessions three times per week. After the week training period following the initial diet intervention, the weight-training group did not ex-perience further weight loss, but maintained the weight lost during the initial week diet period. The aerobic trainers experienced a significant further decrease in weight 2. In addition, there were between-group differences in body composition such that the aerobic trainers lost weight and the resistance trainers' weight remained unchanged.

Trends in fat-free mass were also significantly different in that the weight trainers experienced a trend toward increasing fat-free mass and the aerobic trainers experienced no change in fat-free mass. In the first part of the study, subjects' resting metabolic rate decreased to a greater extent than their weight or fat-free mass. This excessive reduction is most likely attributable to the degree of calorie restriction, and therefore cannot be completely explained by the reduction in fat-free mass.

Wadden and colleagues have concluded that short-term changes in resting metabolic rate are best predicted by baseline resting metabolic rate and degree of calorie restriction, whereas long-term changes in resting metabolic rate are best predicted by baseline resting metabolic rate and fat-free mass. It is not clear how soon after the initial study participants began the second study, or what their dietary intake was during this time.

The mean weights at the start of the second study are 2 kilograms less than at the end of the first study, so it is reasonable to believe that these subjects continued to consume a hypocaloric diet.

As in the first study, diets were not prescribed individually or controlled for adequately in the data analyses. How your GP can help you lose weight How to lose weight in a wheelchair Managing weight with a learning disability. What can I do if my child is very overweight? Underweight adults Underweight adults Keeping your weight up in later life. Underweight teen boys Underweight teen girls Supporting someone with an eating disorder. Underweight children aged 2 to 5 Underweight children aged 6 to Advice for parents of healthy-weight children.

It's not unusual to hear people blame their weight gain on a slow metabolism. Could the culprit be a slow metabolism? What is metabolism? Do some people have a faster metabolism than others? Body size, age, gender and genes all play a role in the speed of your metabolism. Am I fat because of a slow metabolism? Putting a "slow metabolism" to one side, something else may be at play here. Can losing weight too fast slow my metabolism?

Crash diets and other calorie-restricted diets can slow your metabolism. What can I do to speed up my metabolism? The more active you are, the more calories you burn. Here are the 3 most effective ways of burning calories: Aerobic activity Aerobic exercise is the most effective way to burn calories.

But as contradictory as it sounds, all these changes actually result in a more efficient and ultimately healthier metabolism. This can lead to high levels of sugar and fat in the blood, increasing risk of insulin resistance, diabetes, and cardiovascular disease. But without care, this metabolic improvement can conspire against you to regain the weight, and even overshoot your original weight.

Studies show exercise or simply physical activity may be one way to prevent weight regain, by improving our ability to maintain our weight and can potentially minimise metabolic slowing.

Exercise can also help regulate appetite and fuel burning in the short term, and may make weight loss more sustainable in the long term. Portsmouth Climate Festival — Portsmouth, Portsmouth.