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The science of body-weight Lecture 4 & 5 - Coggle Diagram
The science of body-weight
Lecture 4 & 5
Background; Dieting (dietary restriction)
the most common approach to trying to reduce bodyweight is to restrict food intake in some way
whilst dieting might yield results in the short-term, it is less successful in the longer term
WRAP TRIAL
at 1 year, mean weight changes in the groups were - 3.26 kg, -4.75kg and -6.76kg
paritcipants in the behavioural programme lost more weight than those in the brief intervention
the 52 week programme was more effective than the 12 week programme
differences between groups were still significant at 2 years
what happens when undertaking an energy restricted diet?
method & result
44 healthy adult men
measured fasting serum leptin cdoncentration and appetite levels, over a 4 day diet
after 4 days, fasting leptin concentration decreased by 39.4%
Leptin concentration negatively associated with hunger, desire to eat and total appetite
got stronger and stronger across days
conclusions
proportionate reduction in fasting Leptin after 4 days energy restriction
association between decrease in Leptin and increase in hunger/desire to eat
suggest leptin has an important role in resoring energy balance and likely mediated through appetite
helps us to understand role of Leptin
NB. before significant weight loss
what happens when a diet is nutrient-targeted?
method
19 participants
2 week weight-maintaiing diet
2 weeks iso-caloric diet
12 week ad libitum
insulin, ghrelin and Leptin measured
result and conclusions
satiety increased on isocaloric - with no change in leptin
on ad libitum high protein diet - energy6 intake decreased by 411 kcals, body weight decreased by 4.9kg. despite decreased leptin and increased ghrelin
anorexic effect of protein may contribute to weight-loss
TRYING TO REDUCE BODY-WEIGHT - DRUGS
drug treatments
there are three basic mechanisms that drugs act via;
decreasing appetite and caloric intake
increasing energy expenditure
decreasing fat absorption
key terms
agnoist = an agonist binds to the receptor and produces an effect within the cell
antagonist = binds to the same receptor, but does not produce a response, instead it blocks that receptor to a natural agonist
analogue = is a compound having a structure similar to that of another compound, but differing from it in respect to a certain component
LORCASERIN
mechanism of action
serotonin receptor agonist that decreases caloric intake
humans
FMRI study showed that lorcaserin decreases the emotion and saliency-related activity of limbic system, and the activity of parietal and visual cortices in response to highly palatable food cues
HCI, DIETHYLPROPION, BENZPHETAMINE, PHENDIMETRAZINE
mechanism of action
noradrenergic agonists that supress appetite
humans; mechanism of action not completely understood
BUT enhances mainly norepinephrine, but also serotonin and dopamine release in the CNS
PHENTERMINE AND TOPIRAMATE
mechanism of action
the combination of these durgs suppresses appetite
humans; mechanisms poorly understood
phentermine - enhances the release of serotonin, norepinephrine and dopamine
topiramate - GABA agonist, glutamate antagonist and carbonic anhydrase inhibitor
NALTREXONE AND BUPROPION
mechanism of action
both had weight loss as a side effect
rats; bupropion acts on POMC neurons of the hypothalamic ARC and enhances secretion of a-MSH
humans; fMRI showed change in response to food of the hypothalamus and cortical and sub cortical regions regulating self-control, internal awareness and memory.
LIRAGLUTIDE
mechanism of action
liraglutide is a GLP-1 analogue
invloved in blood glucose regulation
slows gastric emptying - increases satiety & fullness
acts on hypothalamus, limbic/reward system and cortex
humans; altered activation in response to images of highly desirable foods
ORLISTAT
mechanism of action
inhibits gastrointestinal and pancreatic lipases
reduced fatty acids absorption
1/3 of fatty acids in food not absorbed
TRYING TO REDUCE BODY-WEIGHT - SURGERY
what is Bariatric-Metabolic surgery?
causes weight loss via
restricting amount of food the stomach can hold
malabsorption of nutrients
or a combination of both
often causes hormonal changes
TYPES OF SURGERY
GASTRIC BYPASS
roux-en-Y gastric bypass
considered the gold standard
small stomach pouch is created
beginning of small intestine divided and one part is brought up to meet the new stomach pouch
SLEEVE GASTRECTOMY
laparoscopic sleeve gastrectomy - 'the sleeve'
removal of about 80% of stomach
creates a tubular pouch
particular effect on gut hormones
ADJUSTABLE GASTRIC BAND
'the band'
creates a small stomach pouch via the use of an inflatable band around the upper-part of the stomach
a port allows for the filling of the band with saline
BILIOPANCREATIC DIVERSION WITH DUODENAL SWITCH GASTRIC BYPASS
BPD/DS
first part similar to a sleeve gastrectomy
second part involves the bypassing of a large section of the small intestine
Bariatric surgery and Ghrelin
decrease in ghrelin levels following vertical sleeve gastrectomy and rouz-en-Y gastric bypass
mechanism - removal/exclusion of gastric fundus
variability likley due to differential exclusion
Ghrelin changes MIGHT underpin post-surgery changes in decreased liking of palatable food, new food aversions and changes in taste and smell
ghrelin increase after diet induced weight loss and adjustable gastric band surgery
BATRIATRIC surgery and Leptin
leptin tends to decrease following surgery
evidence suggests the decrease is in line with weight loss
this finding is in line with the idea that because adipose tissue secretes leptin, as volume of adipose tissue decrease so does leptin
EFFECTS OF OBESITY
obesity and overweight are associated with a plethora of co-morbidites including
cardio-vascular disease
type 2 diabetes
some cancers
is there a relationship between obesity and cognitive function?
areas where evidence supported a link;
intellectual functioning
psychomotor performance
speed
visual construction
concept formation
setshifting
decision making
areas where evidence was equivocal;
visual memory
verbal memory
complex attention
delay discounting
inhibition
areas where there is NO evidence of link;
general cogntive perofrmance
time judgement
working memory
verbal fluency
Critical thinking about this literature
many of the studies failed to account for confounds such as age, education, depression...
many studies did not use proper exclusion criteria (e.g substance misuse)
lack of comparison groups (use of normative groups not matched groups)
publication bias
quality of assessment tools varied
lack of broad assessment of cognitive domains
why might this be? LEPTIN?
Leptin has been associated with impaired cognitive performance
Leptin associated with many different functions in the brain (aside from energy homeostasis)
leptin infleunces hippocampal-dependent learning and memory
leptin has been shown to have anti-depressant properties
why might this be? INFLAMMATION?
inflammation is associated with obesity
inflammation also causes neuronal dysfunnction via microglia
associated with subtle cogntive deficits
Balter et al. wanted to test whether these factors are inter-related
CORRESPONDENCE IN FOOD ADDICTION?
tolerance; increasing amounts of food needed to be satisfied
distress and dysphoria during eating
persistent desire for food and unsuccessful attempts to curtail amount eaten
great deal of time spent eating
overeating continued despite knowledge of problems caused by excessive food consumption
clinical features of substance addiction
withdrawal symptoms
important activites given up
continued use even when problems in relatinships
giving up important socail, occupational, recreational activites
not linked to criminal behaviour
overlapping neural substances
dopamine is released when drugs are taken anda released when weanticpate or actually eat
sensitisation is seen over time leading to increased wanting of food/drugs
BUT; dopamine release habituates quickly for food, different sub-populations of neurons in nucleus accumbens stimulated by drugs vs. food
neurobiological evidence for food addiction
some similiarites but also differences
food loacks the motivational intensity of drugs of abuse