The science behind weight loss

In most cases, the science behind being overweight comes down to a matter of energy balance. Excess fat is stored when people take in more energy (through food and drink) than they are using up in physical activity.

Our current environment means that it is easier to gain weight than it used to be. We have access to cheap, processed foods that are high in calories and we tend to do less physical activity in our daily lives. This has led to increasing numbers of people becoming overweight.

Shifting the Energy Balance Back

If we can reduce the number of calories that we take in, and increase our levels of physical activity, we can shift the energy balance back in favour of a healthy weight.

What are calories? click here
  • In general, most women will lose weight if they eat or drink between 1,200 and 1,500 calories per day.
  • Most men will lose weight if they eat or drink between 1,500 and 1,800 calories per day.
  • However, some people might find they will initially lose weight at a higher number of calories than this, if their starting daily intake of calories was greater to begin with.

Daily Nutritional Requirements for Weight Loss:

Requirements per day Men Women
Energy as Calories (Kcals) 1500-1800 1200-1500
Fat (g) 58-70 46-58
Saturated Fat (g) 16-20 13-17

Maintaining a healthy weight

When you have reached your target weight, you may need to adjust your calorie intake to ensure that your weight remains stable in a healthy weight range. Generally, a healthy weight range can be defined as a BMI of 18.5-25.

Weight Loss Maintenance

We can think of weight management as two phases: a weight loss phase and a weight loss maintenance phase.

During the first phase (usually lasting three to six months) a weight loss occurs, followed by a second phase where ideally the weight is maintained1. However, for many people the weight is slowly regained. Researchers have provided lots of evidence and recommendations on how people can lose weight but less is known about how they can they can keep the weight off successfully2.

What is “weight loss maintenance”?

If you are overweight, losing a moderate amount of weight (5-10% of your starting weight) can bring significant health benefits 3, 4. However, to maintain those health benefits it is important to keep the weight off. This goal can be a challenging and a difficult process.

According to some studies, the difficulty associated with weight maintenance could be related to the natural process of our body to regain the lost weight,5 but also to psychological causes such as going back to old unhealthy dietary habits and sedentary lifestyles6. However, our weight rarely stays exactly the same and could fluctuate for many reasons, including: fluid retention during a menstrual cycle and water fluctuations after activity7

  • It can be helpful to set a limit of how much your weight can go up. For example, a weight change within 3% of your current weight can be expected to occur7.
  • If your weight increases past this, then it is probably a sign that you have started to put weight back on again.
  • After finishing your weight management programme, set your upper weight limit and try not to pass it. For example if your weight is 100kg, your upper weight limit would be 103kg.

Barriers to keep the weight off

Successfully keeping the weight off is associated with several psychological factors. For example, research has shown that people are less likely to keep the weight off8 when they:

  • eat when they are stressed or sad
  • have set unrealistic weight loss goals
  • consider their inability to reach their target weight as a failure
  • have negative feelings about their body

What can I do to keep my weight off?

Several strategies can help us keep our weight off. These strategies can be related to the way we are thinking but also to our lifestyle habits.

One of the great sources of information for weight maintenance is the National Weight Control Registry established by R.Wing and O.Hill in 19949. The National Weight Control Registry aims to collect information regarding successful weight loss maintenance, they reported that people who can keep their weight the same are the people who10:

  1. Check their weight at least once per week. Monitoring our weight regularly provides an opportunity to reflect on how our lifestyle is affecting our weight and allows us to take action before our weight changes significantly11.
  2. Continue to eat a low fat diet. Studies report that successful weight maintenance is related to a low consumption of fat12. Consumption of a low fat diet leads to consumption of less energy or less calories13. This may help to prevent weight gain14.
  3. Eat breakfast every day. Having breakfast daily can help us regulate our appetite better, feel less hungry between meals and eat less as a result15. The benefits could increase when our breakfast includes foods that are rich in fibre16.
  4. Be active by watching less than 10 hours of TV per week and exercise for 1 hour per day. Several studies and clinical guidelines support that physical activity plays an important role in the maintenance of reduced weight3, 4, 17. Although there is no general agreement about the level and amount of physical activity18 and even though some studies suggest that weight control is a much more complicated process than just an issue of physical activity, research shows that being active increases our energy expenditure19 and can improve cardiovascular health20.

What do the Clinical Guidelines say?

According to clinical guidelines National Institute for Health and Clinical Excellence (NICE) (2006) and Scottish Intercollegiate Guideline Network (SIGN) (2010):

  • It is important for weight management services to support individuals to develop skills for weight loss and weight loss maintenance.
  • Individuals are more likely to maintain a healthy weight if they consume a healthy balanced diet and have an active lifestyle (30 minutes of moderate physical activity, five days per week).
  • However, individuals who are overweight or obese may need to do more exercise during the day than the recommended amount of 30 minutes per day.

To sum up

“Weight loss maintenance” is a challenging process but very important. Maintaining the weight that we have lost means that we have made sustainable lifestyle changes that can help to protect us from future health risks. Successful weight loss maintenance is influenced by our healthy dietary habits and our regular physical activity patterns. Mechanisms that can support weight loss maintenance include regular monitoring of our weight.

References

1. Jeffery RW et al. Long-term maintenance of weight loss: current status. Health Psychol 2000,19:Suppl:5-16
2. Sciamanna C et al. Practices associated with weight loss versus weight-loss maintenance results of a national survey Am J Prev Med, 41 (2) (2011), pp. 159–166
3. National Institute for Health and Clinical Excellence (NICE). Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children. NICE 2006, London.
4. Scottish Intercollegiate Guideline Network (SIGN). Management of obesity: a national clinical guideline. SIGN 2010, Edinburgh.
5. Rosenbaum M, et al. Low-dose leptin reverses skeletal muscle, autonomic, and neuroendocrine adaptations to maintenance of reduced weight. J Clin Invest. 2005,115(12):3579–3586
6. Wing RR, Hill JO. Successful weight loss maintenance. Annu. Rev. Nutr. 2001, 21:323-341,.
7. Stevens J, Truesdale KP, McClain JE, Cai J. The definition of weight maintenance. Int J Obes (Lond) 2006, 30:391-399
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9. National Weight Control Registry. Available at : http://www.nwcr.ws/
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11. Butryn ML, Phelan S, Hill JO, Wing RR. Consistent self-monitoring of weight: a key component of successful weight loss maintenance. Obesity (Silver Spring) 2007,15:3091-3096
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13. Rolls BJ. The relationship between dietary energy density and energy intake. Physiol Behav. 2009, 97:609–615
14. Hill JO 2006 Understanding and addressing the epidemic of obesity: an energy balance perspective. Endocr Rev 27:750–761
15. Timlin, M. T., Pereira, M. A. Breakfast frequency and quality in the etiology of adult obesity and chronic diseases Nutrition Reviews 2007, 65 6 pt. 1 268–281.
16. McCrory MA, Campbell WW. Effects of eating frequency, snacking, and breakfast skipping on energy regulation: symposium overview. J Nutr 2011
17. Catenacci VA, Wyatt HR. The role of physical activity in producing and maintaining weightloss. Nat Clin Pract Endocrinol Metab 2007, 3(7):518–29.
18. Donnelly JE et al. The role of exercise for weight loss and maintenance Best Pract Res Clin Gastroenterol 2004, 18, pp. 1009–1029
19. Jakicic JM. The effect of physical activity on body weight. Obesity (Silver Spring). 2009,17(suppl 3 3s):S34–S38
20. Cook CM, Schoeller DA: Physical activity and weight control: conflicting findings. Curr Opin Clin Nutr Metab Care 2011, 14(5):419-424.