satiation/satiety hormones released from the gut & act via the circulation or the vagus nerve on hypothalamic centers
GLP-1 (Glucagon-like peptide 1)
causes gastric emptying to slow down (“ileal brake”)
secreted by the small intestine in response to the presence of macronutrients in the ileum
promotes satiety via the hypothalamus
is an incretin hormone: accentuates the pancreas' insulin response to blood glucose
stimulating gallbladder contraction in response to protein & fat in the duodenum
also contributes to cessation of eating by action on hypothalamic centers and by delaying gastric emptying
Where are sensory properties before and during food ingestion integrated in the brain?
the orbitofrontal cortex
What role does the midbrain play in the non-homeostatic way food Intake is controlled?
the midbrain is where the metabolic properties of the food, including its ability to provide energy substrates & the hormonal response to intake (as transduced via the hypothalamus) are translated into reward
What kinds of food appear to be superior in inducing reward?
1. foods that provide larger amounts of energy (i.e. more energy dense foods)
2. foods that lead to rapid rises in blood glucose
non-homeostatic regulation of intake can overcome homeostatic control for ingestion of food with high reward value --> why high fat or high sugar foods are consumed beyond energy needs
protein produced in fat cells (in proportion to amount of fat stored) secreted into the circulation where it travels to the brain, crosses the blood brain barrier, & acts on the hypothalamus to DECREASE food intake
higher amounts of body fat are associated w/ higher blood concentrations of leptin
in RODENTS (not humans) leptin stimulates energy expenditure
What affect does leptin have on someone who's obese?
while leptin concentrations in obese persons are appropriate for the amount of body fat, the action of leptin is impaired, suggesting resistance to leptin action in the brain
What is the effect of a leptin deficiency due to genetic mutations?
such cases result in severe obesity at a young age
occur very rarely in humans
leptin injections in deficient individuals reverses obesity, however for those who are NOT leptin deficient, leptin injections have only a very modest and inconsistent effect on reducing weight
A defect in what receptor is associated with binge eating in obese people?
the melanocortin 4 receptor, which is involved in leptin signaling in the hypothalamus
this defect is present in approximately 5% of severely obese persons
reduces blood glucose in the periphery (body tissues outside of the central nervous system)
if glucose concentrations dip too low one of the responses is hunger
What happens when insulin is injected into the cerebral ventricles?
food intake DECREASES
high insulin levels are an indicator that body fat stores are adequate --> no need for anymore eating
What are high levels leptin or insulin levels indicative of?
that body fat stores are adequate
in this state mechanisms that control food intake in the short term are accentuated
Leptin and insulin act by modulating short term hunger & satiation/satiety signals
especially soluble fibers, increase stomach distention, which activates afferent vagal nerve signals of fullness to the brain
soluble & insoluble fibers also act as a physical impediment to digestion
delayed carbohydrate digestion and absorption blunts blood sugar rise with intake, leading to a blunted insulin response
undigested nutrients trigger secretion of the gut hormones like GLP-1 and thus cause slowed gastric emptying and prolongation of sensations of fullness
High protein, low carbohydrate Diets
protein has been shown to be more satiating and slow the return of hunger in comparison to other macronutrients
protein seems to be better at satisfying hunger than refined carbs partly b/c it doesn’t induce large fluctuations of blood glucose
proteins are digested more slowly, sending nutrients into the blood stream over hours
What is likely to be a factor that contributes to satiation after high protein intake?
Stimulation of CCK
Glycemic index (GI)
the increase in blood glucose following consumption of a standardized amount of carbohydrate in comparison to the increase observed with consumption of white bread or glucose (set at 100)
foods with a lower glycemic index reflect slower digestion & absorption of glucose from food; lower GI foods result in a lower insulin response
Glycemic Load (GL)
a calculation of the total GI of the diet with consideration of the amount of each food eaten and the total carbohydrate of the diet
What are some determinants of a food's glycemic index?
Carbohydrate content + type
Higher GI: sucrose, glucose, amylopectin
Lower GI: fructose, amylose
Food structure and form
Degree of cooking
Presence of other substances that influence gastric emptying, digestion or absorption (eg. fiber or fat)
High fat diets tend to be ____ energy dense
high fat = MORE energy dense diet since fat has over twice the energy
per gram in comparison to other macronutrients
when diets of higher and lower fat have the same energy density, equal volumes of each diet are consumed
What may now be one of the biggest challenges to our weight control?
Continuously available food
Large portion sizes can be viewed as a type of increased food availability; larger portions lead to greater intake regardless of hunger or desire to eat
Eating a higher variety of low energy foods such as vegetables is associated with ________, whereas eating a high variety of high-energy foods such as sweets, snacks, entrees is associated with _______
more variety of low E foods: LEANNESS (presumably through reduction in energy intake)
more variety of high E foods: FATNESS
Post Ingestive Conditioning
there is a direct relationship between preferences for common foods & kcal/gram
rat studies showed that digestion and absorption impact food preferences more than food taste
if rats are given food tasting of vanilla that has few calories & it is allowed to pass into the stomach and then be absorbed in the intestine, they may eat SOME of the food at future occasions
if the vanilla food is fed but is then removed from the esophagus via the cannula & replaced by a higher calorie food w/out vanilla that is placed the stomach via the cannula, rats will eat MORE of the vanilla food than in the 1st condition
if rats eat the vanilla food & it is removed so that no food reaches the stomach, the rat will soon eat LITTLE vanilla food
Nutrition 4 - Obesity
the gain in fat & fat free mass due to positive energy balance, energy intake in excess of energy expenditure
generally w/ positive energy balance, about 3/4 of gained weight will be fat, while the remainder will be fat free mass including structural protein & water weight
What is the effect of obesity on basal energy expenditure (BEE)?
it slightly increases in response to excess intake, but only by 5-10% of the excess energy intake
therefore BEE will not dissipate most of the excess intake
TEF: the thermic effect of feeding increases only in proportion to ingested energy so is NOT considered adaptive
NEAT: non-exercise activity thermogenesis may increase substantially & appears to limit weight gain
How can obesity cause disease?
Promotion of pro-thrombotic state (increased coagulation of blood)
Physical stress on joints & tissues
Increased blood volume
Psychosocial issues and discrimination
What often improves weight-related morbidities?
a loss of 5-10% of initial weight
weight loss beyond this range is difficult, therefore an initial goal of 5-10% of weight over 3-6 months is reasonable
What do some fad diets & weight loss supplements claim?
that on such plans little or no FFM is lost and all lost weight is fat; these claims have NOT been substantiated
the average composition of tissue lost 65-75% fat mass & 25- 35% fat free mass
What is the most effective measure of weight loss?
the % of initial weight that was lost
other less effective measures include absolute terms (pounds or kgs) or change in BMI
low cal diets: 5-10% of initial weight lost
VERY low cal diets: 15% of initial weight
exercise without diet change: 1-2%
addition of exercise to diet change: additional 1-2%
Behavior therapy added to diet & exercise: additional 2-5%
Meds: about 3-5% more than diet and exercise, or 10-15% of initial weight
Surgery: 15-35% of initial weight
very low calorie (VLCD): < 800 kcal/day
low calorie diets: > 800 kcal/day
“Moderate” diets: deficits of 500 kcal/day below maintenance of energy needs
generally a deficit of 500 kcal/day leads to a loss of 1 pound/week
Very low calorie diets (VLCD)
consumed for 3-6 months
are usually products such as shakes & bars that are consumed 5-6 times/day
they require regular medical monitoring due to risks including: dehydration, electrolyte disturbances (eg. hypokalemia, low potassium), cardiac rhythm disturbances (rare but due to electrolyte
disturbances), or Gallstones
What do all weight loss diets carry some risk of?
the rate of weight loss is a primary determinant of gallstone formation
Low calorie diets (LCD)
have an average weight loss is 8% of initial weight over 3-6 months
to achieve weight loss there must be long-term adherence to a diet that promotes negative energy balance
The Zone Diet
most often employed for weight loss but need not be limited to this
it is based on a carbohydrate to protein to fat energy ratio of 40:30:30
it's based on the idea that less insulin secretion is fundamental to weight loss & health benefits achieved by diet
What foods are recommended & discouraged on the Zone diet?
recommended: whole grains, fish, nuts, olive oil
discouraged: refined grains, meat are
The South Beach Diet
based on restriction of carbohydrates & some fat types
is usually employed for weight loss
the initial phase restricts bread, pasta, potatoes, rice, fruit, & foods w/ added sugar; lean meat & some vegetables ARE consumed
diet is later advanced to include lean protein, low fat dairy, & some whole-grain carbs & fruit
the last phase includes whole grains, vegetables, & fruit
The Atkins Diet
a low carb diet primarily employed for weight loss; it features intake of protein and fat
it discourages intake of foods with saturated fat but healthier fats are encouraged (*in practice it can include a high intake of saturated fat)
over time the amount of carbs is increased to a level consistent with weight maintenance
*this diet can be insufficient in water soluble vitamins & some minerals
Increases in physical activity provide multiple benefits that complement diet changes:
reduced risk of cardiovascular disease, diabetes, & mortality
maintenance of FFM during weight loss (happens more w/ weights v. aerobics; BEE may not be maintained to the same extent)
improved self-efficacy (the belief than one can change behavior) & mood
are considered for those who do not meet weight loss goals & who have BMI > 30 kg/m2 or BMI > 27 kg/m2 WITH weight-related conditions (eg. dyslipidemia, hypertension, sleep apnea, or heart disease)
meds + lifestyle change improves weight loss by 3-5% of initial weight + that achieved by only lifestyle change
can also help maintenance of lost weight by preventing regain
a drug that acts on the central nervous system to suppress appetite
it influences brain neurotransmitters (like serotonin, norepinephrine)
There are no approved or safe drugs that act primarily by increasing what?
energy expenditure, or that increase thermogenesis
medication that inhibits gastric and pancreatic lipase, which decreases hydrolysis of dietary fat by up to 30%
fat that is not absorbed will be excreted
inhibiting fat absorption may also decrease absorption of fat soluble vitamins
When would surgery be considered to combat obesity?
for those with BMI > 40 kg/m2
or 35 kg/m2 w/ weight-related comorbidities
*surgery is the only option demonstrated to result in long-term weight loss, long-term improved weight-related comorbidity, & reductions in mortality*
the stomach size is reduced by partitioning (stapling) or by creating
restriction with an adjustable band
by bypassing part of proximal small intestine, food does not meet
digestive enzymes and does not become available for absorption until further downstream in the small intestine