Myths, Presumptions and Facts about Obesity

Transcription

1 1 Myths, Presumptions and Facts about Obesity Cátia Martins Associate Professor Obesity Research Group IKOM, Faculty of Medicine NTNU 2 Myth believe held true despite the existence of substantial refuting evidence. Presumption - believe that is held to be true, but for which convincing evidence does not yet exist to confirm or to disconfirm their legitimacy. Fact - proposition backed by sufficient evidence to consider them empirically proved for practical purposes. 1

2 3 The link between obesity and health Characteristics of obese individuals Causes of obesity Obesity treatment strategies 4 1. Body weight is a measure of good health McAuley & Blair, 2011 (J Sports Sci); Salas, Forhan & Sharma, 2014 (Clin Obes) 2

3 5 2. Obese people are all lazy and sedentary Colley et al, 2011 (Health Rep) 6 2. Obese people are all lazy and sedentary Obese adults may have lower PA levels than normal-weight controls, but not necessarily lower PA energy expenditure Obese individuals spend more energy for the same volume of exercise compared with normal weight controls, particularly for weight bearing exercise Overweight/obese individuals may experince greater environmental, medical and emotional barriers to being more physical active Is physical inactivity a cause or a consequency of obesity?! Salas, Forhan & Sharma, 2014 (Clin Obes) 3

4 7 8 4

5 9 10 5

6 11 3. All obese people eat unhealthy diets The nutritional quality of the diets consumed by obese individuals is not significantly different from that of normalweight individuals Obese individuals may consume healthy or unhealthy diets, as their normal weight peers! It is important not to make assumptions about the dietary habits of an obese individual. But obese eat more (higher EI) than normal-weight individuals (when in energy balance) Salas, Forhan & Sharma, 2014 (Clin Obes) Obese people have a low/slow metabolism - Low resting metabolic rate (RMR) Basis for conjecture: - Free fat mass (FFM) is the main determinant of RMR - Obese individuals have a lower % FFM as compared to normalweight individuals BUT 6

7 13 4. Obese people have a low metabolism - Low resting metabolic rate Resting metabolic rate increases progressively with body weight. Obese individuals (as a group) have a higher overall RMR compared with normal-weight (but a lower RMR/kg body weight!) Obese people have a low/slow metabolism - Hypothyroidism Basis for conjecture: - There is an inverse correlation between free thyroxine (ft4) values and BMI - Both subclinical and overt hypothyroidism are frequently associated with weight gain, decreased thermogenesis, and RMR BUT Biondi B, 2010 (J clin Endocrinol Metab) 7

8 15 4. Obese people have a low metabolism - Hypothyroidism Thyroid hormone levels have been reported to be normal, increased or decreased in obese patients The majority of obese people does not suffer from hypothyroidism Hypothyroidism leads only to minor weight gain Maybe obesity is a cause (not a consequence) for incresed T3 Biondi B, 2010 (J clin Endocrinol Metab) Snacking contributes to weight gain and obesity. Basis for conjecture: Snack foods are presumed to be incompletely compensated for at subsequent meals, leading to weight gain But. Observational studies do not shown a consistent association between snacking and obesity or increased BMI. RCTs have produced contradictory results Casazza et al, 2013 (NEJM) 8

9 17 6. Regularly eating (versus skipping) breakfast is protective against obesity. Basis for conjecture: Skipping breakfast purportedly leads to overeating later in the day But obese people tend not to eat breakfast Cause or effect?! The available evidence from RCTs is insufficient to make causal claims about skipping breakfast itself independently affecting obesity. Those successful in maintaining weight loss in the long-term eat breakfast regularly Casazza et al, 2013 (NEJM) Small sustained changes in EI or EE will produce large, long-term weight changes. Basis of conjecture: National health guidelines and reputable websites advertise that large changes in weight accumulate indefinitely after small sustained daily lifestyle modifications daily EE by 100 kcal by walking 1 mile/day (1.6 km) will lead to a WL > 50 lb (22.7 kg) over a period of 5 years The true WL ~ 10 lb (4.5 kg), assuming no compensatory in EI, because changes in body weight alter energy requirements... Casazza et al, 2013 (NEJM) 9

10 19 8. Losing weight quickly is associated with negative health outcomes - Greater loss of FFM - Larger weight regain Basis for conjecture: reaction to the adverse effects of nutritionally deficient VLEDs in the 1960s Several reviews and meta-analysis have shown that a greater initial weight loss is associated with a better weight loss maintenance in the long-term Casazza et al, 2013 (NEJM) 20 Purcell et al, 2014 (Lancet Endocrinol Metab) 10

11 21 Purcell et al, 2014 (Lancet Endocrinol Metab) Daily self-weighing is detrimental for weight management Basis for conjecture: for a person trying to lose weight, seeing his/her weight go in the direction opposite to their efforts can be discouraging. But several experimental studies have shown that daily selfweighing, on its own, produce a significant weight loss People who weight themselves daily are more likely to succeed at losing weight, maintaining their weight after weight loss treatment and preventing weight regaining than those who do not weigh themselves daily Casazza et al, 2014 (CRFSN) 11

12 Weight cycling (i.e., yo-yo dieting) increases mortality Basis for conjecture: In observational studies, mortality rates have been lower among persons with stable weight than among those with unstable weight Findings are probably due to confounding by health status Recent studies find no compelling evidence that weight cycling, defined in terms of intentional weight loss followed by regain, is associated with excess mortality risk Long-term RCT are unavailable and unethical to perform but studies in animal models do no support the epidemiological association Casazza et al, 2013 (NEJM); Casazza et al, 2014 (CRFSN) 24 What to do then? Myths should be abandoned Presumptions should be tested whenever possible with the golden standard procedure: RCT We (health professionals and the scientific community) need to be open and honest about the real status of our knowledge! 12

13 25 References: Salas, Forhan & Sharma, Clin Obes, 2014; 4: McAuley & Blair, J Sports Sci, 2011; 29(8): Casazza et al, NEJM, 2013; 368 (5): Casazza et al, Crit Rev Food Sci Nutr, 2015;55(14): Wadden et al, Obesity, 2009; 17(4): Why do we think and/or claim we know things that we actually do not know? QUESTIONS? 13