Obesity III Flashcards
How should we treat obesity?
*The best thing we can do is to ensure that people do not become obese in the first place -prevention is best
Dieting and obesity surgery may work but they’re very high cost
Dieting isn’t always successful
Instead of making big changes to one person, its better to make small changes to a lot of ppl = PREVENTION
What are 5 treatment options for obesity? And what does the strategy employed depend on (3)?
–Diet
»1200 different diet books on the market
»Over 70% of adults claim to have tried one or more diet
–Exercise (guidelines and effectiveness)
–Behaviour therapy (aiding change and preventing relapse)
–Drugs (limited choice at present)
–Surgery (most effective option)
*The type of strategy employed depends upon three things; age, health and BMI
How do diets work?
*As we know the cause of obesity is energy intake (eating) exceeding energy expenditure (exercise etc)
*The most obvious strategy is to reduce energy intake -that is to diet
–These range from the evidenced-based to the farcical
–Most commercial diets have no evidence base
–All diets that work, work in the same basic way –they reduce the amount of energy you are consuming
–This then leads to a state of negative energy balance
–The body then starts to burn its fat supplies and so weight loss begins
What are 7 parameters that a diet can play with?
*There are really only a limited set of parameters that any diet (that might reasonably work) can play with
–The principal variable is macronutrient content
*That is the proportion of fat, protein and carbohydrate in the diet
*One could also add in here whether you are preparing the food or whether it is being prepared for you
–Glycemic index
–Solid versus liquid
–Portion size modification
–Eating rate modification (chewing rate)
–Energy density (low energy density diet –high fibre water content)
–Fasting
What does a diet need to do?
*Irrespective of what is being modified, to be effective a diet needs to get you eating around 14-1500 Kcal/day
*Even if this diet consisted of big macs and fries, if it is 141500 Kcal/day you will lose weight
What are 5 successful diet types?
*Low Fat (the nutritional gold-standard; Jenny Craig, Weight Watchers; Very-low fat diets –Pritkin, Ornishdiets)
*Emphasising high Protein (Zone, Paleodiets)
*Emphasising low Carbs (Atkins, Sugar Busters, South Beachdiets)
*Low Glycemic index (GI)
*Mediterranean diet (good fat, limited meat, high fruit, veg & fish)
What is a fat reduction diet?
*Fat is the most energy dense macronutrient
*Therefore, reducing each gram of fat in a diet has more effect (in terms of reduced energy intake) than reducing equivalent amounts of protein or carbohydrate
–Traditionally, it was also thought that removing saturated fats would yield additional health benefits
*For these reasons low fat diets have been the traditional approach adopted by nutritionists and are the mainstay of most medical interventions
–They are also important commercially
*Not surprisingly then, they are the best studied
How do you evaluate a diet? (4 + low fat diets)
*To evaluate a diet program we need three key things
–A good sample size (500+ because of attrition to follow up & effect size)
–A treatment and a control group (an appropriate control is tricky to design –similar level of contact, information, motivation etc)
–Random allocation to these groups
*Success is generally defined as a loss of 5% of initial body weight at one-year (contrast this with peoples expectations which is 1/3 of initial body weight or about 30% weight loss!)
*Three large scale trials have evaluated low fat diets and there have been multiple small scale trials of several commercial programs that can be pooled for meta-analysis
*A low fat diet is defined here as obtaining around 20% of your energy from fat
*With a target of 1500Kcal/day –that is 30g of fat/day
–Contrast this with the average US diet of 2200Kcal/day
–Of which 35% of energy is from fat (i.e. 85g of fat/day)
–That is a bigchange!
Do fat reduction diets work?
*In these three studies participants were evaluated at 6 months (2 studies) and 12 months (1 study) -all worked
Very diff weight loss between ctrl and treatment grs
*These parallel findings from studies of Weightwatchers and Jenny Craig in terms of effectiveness
All around 5% weight loss
What are very low fat diets? (4)
*People who are morbidly obese may require more drastic dietary interventions
*May be used as a test of motivation for surgery and to get weight down to a level where the person will survive anaesthesia
*These are commercially available too (e.g., Pritkin, Ornish, Medifast, OPTIFAST)
*One which has been commonly used is to reduce energy intake from fat to less than 5% with then an overall energy intake of around 1000-1200Kcal/day
*These diets result in larger initial weight loss (10kg at 6 months), but weight regain over 1-5 years may make them no more efficient (long term) than low-fat diets
*Note fewer & smaller studies (n < 100; so less reliable)
*May also produce additional gains for coronary artery stenosis
What are the conclusions about fat reduction diets? (4)
*They work -but they are hard work
*Fat makes food palatable, its loss impacts on the pleasure obtained from eating
*However, low fat dieters often claim they have too much food!
*An additional benefit is that LF diets may alter preference for fat
*A further consideration is the type of fat consumed
*Although low fat diets reduce energy intake, diets that concentrate on eating good fats (mono and poly-unsaturated fats) can also produce additional health gains, such as reduced cholesterol, coronary artery stenosis and glucose tolerance
*One example is the ‘Mediterranean’diet which combines ‘good’ fats, with an overall healthy diet
What is a Mediterranean diet? (7)
*Although the diet is pretty similar in fat content to a North American diet it differs in several important ways
–‘Good’ fats such as olive and fish oils predominate
–High in fibre
–Main source of energy is low GI carbohydrates
–Limited red meat
–Lots of fruit and vegetables
*Unfortunately, there have been very few clinical trials of the Med diet, so it is hard to discern its effects on body weight (i.e., as a diet tool)
–Epidemiological studies suggest that this type of diet is associated with lower risk of heart disease, longevity (Ancel Keys lived to 100) and better cognition into old age
*Some other regional diets may offer similar benefits, such as the traditional Japanese diet high in complex carbohydrates and fish
–There must be something beneficial to it, as there are over 60,000 centenarians in Japan –3X more % wise than in the USA
What are high protein diets?
High protein diets (e.g., Zone or Paleo diet) essentially up protein levels, at the expense of fat and especially carbs
–The Paleo diet is based on the dubious premise that we should eat what our ancestors ate (i.e., the diet we are ‘optimally’ adapted for)
–Unfortunately, there is a lot of uncertainty over what they ate, and even when they ate the same food is probably different now (e.g., fat profile and content of wild vs farmed meat)
Far fewer studies have been conducted on this type of diet, none of which meet our ‘strict’ criteria
*The best one available allocated 50 overweight and obese individuals to two diets, both equivalent and low in calories
*One diet was low in protein (Energy: 12% protein, 30% fat, 58% carbs)
[note dietary guidelines suggest 18% for protein]
The other was high in protein (Energy: 25% protein, 30% fat, 45% carbs)
*All the food was provided to ensure compliance for the first 6 months (6-12 months self-preparation)
Do high protein diets work? (6)
*The high protein group lost more at 6 months (9.4Kg) than the low protein group (5.9Kg)
–At two years, there was no significant difference in weight loss
–However, many subjects were lost to follow-up (power)
–Trend for greater weight loss remained
*The high protein group demonstrated additional gains, notably a greater reduction in abdominal fat
–This gain was maintained to follow-up
*These results are comparable in magnitude to low fat diets, a key question is whether it is easier for someone to maintain them
*Extra weight loss might result from greater satiation produced by the high protein diet
What are low carb diets? (4)
*In this class of diet (e.g., Atkins, Sugar Busters, South Beach) the primary aim is to especially reduce carbs and up protein (and fat) intake
*The Atkins diet is the most well known example
*Atkins claims 20M people have used his diet
*According to Atkins no dietary restriction is required as the nature of the food (protein) result in excess weight loss
*This is untrue -it works like all other diets -calorie restriction
*Several studies have now examined low carb diets, most by comparing them to low fat diets
–The conclusions are based on meta-analysis of lots of small scale studies, so the evidence base is weak
*They are as effective as low fat diets, but they may have a slight edge (easier change)
*The evidence is not complete as there have not been sufficient large scale trials to decide whether low carb diets are really superior to low fat diets
*This is a hotly debated issue
–Some claim that the extra weight loss is produced by the water needed to metabolise the extra dietary protein
–Stop the diet and the water comes back and weight loss is then the same as low-fat diets
*In addition there are some safety concerns
*These are not well understood and may include
–Renal failure and osteoporosis
–Unsuitable for certain patient groups (high BP & Kidney disease)
–Long term costs vs benefits not evaluated
–Could increase the risk of heart disease
