Chapter 2A That Looks Good

Appetite, hunger, and satiety

The physiology of appetite

Fitting into your genes

Appetite Mission Control: Cell signals

Homeostatic control

Energy balance

Table: Factors that control appetite

Fatmouse: The discovery of leptin

Hedonic control

Visual stimulation – environmental chapter?

Appetite, hunger, and satiety

In following chapters we’ll look more at the various elements that shape our hunger, appetite, and satiety. But let’s start by understanding just what these things mean.

Appetite, as we’ll learn more about in Chapter 3, is wanting to eat and a desire for food – “I feel like eating”.

Hunger is a physical sensation: feeling headachey and irritable; feeling weak; stomach growling (known as borborygmus, which is one of my favourite words – it sounds to me like a good name for a troll in Slavic folklore, i.e. “Children were warned to stay away from Borborygmus the Gnasher, who lived deep in the forest.”), etc.

Satiety is a physical and cognitive sense of fullness or “meal done-ness”. Satiety is somehow knowing that we should stop eating.

Appetite, hunger, and satiety are both primal and sophisticated experiences.

Appetite in particular is a complex socio-psycho-biological phenomenon, which means that it’s shaped by complicated relationships between:

  • primal survival mechanisms in our bodies;
  • our higher-order thoughts;
  • our often-messy emotions;
  • our frequently-unreliable memories; and
  • the weird and wonderful people and things around us.

To give you an example, let’s say you’re having dinner with your new girlfriend’s or boyfriend’s snooty overbearing parents for the first time.

  • Primal survival mechanisms: You’re feeling anxious and fearful – what if they hate you? What if you make a horrible faux pas? Your amygdala – your primal brain’s fear centre – is revving its engines at the potential threat. Your body is coursing with adrenaline and cortisol, your primal fight-or-flight hormones, which will kill your appetite in the short term, but quickly turn you into a ravenous beast after the blood sugar blast clears. During cocktail hour you weren’t hungry, but now you are starving.
  • Higher-order thoughts: You’re focused on which spoon and fork to use. Wait – work from the outside in, or inside out? Oh great, oysters? Which bloody utensil am I supposed to use for that? You consider skipping this course.
  • Emotions: You are madly in love with said girl or boyfriend and don’t want to let them down. You fear offending Mr. and Ms. Snootwhistle. You’re happy that the relationship has gotten this far. Your stomach is full of butterflies trying to smash their way out of your ribcage, as various gut hormones that act as neurotransmitters compete for supremacy.
  • Memories: Hey! You remember which fork to use for oysters! Thank heaven for finishing school! Now you can tuck in to that plate of invertebrates.
  • Social and physical environment: Mr. Snootwhistle – while smoking a smelly cigar – is expounding in grisly detail on his rare elephant poaching while on safari; Ms. Snootwhistle is quietly chugging Scotch; your paramour is stroking your knee under the table. You’re eating off the good china and you’re almost afraid to touch it.

See? Complicated.

Like appetite, satiety is also complicated. Many people, for instance, either can’t feel their satiety signals or choose to ignore them. They just keep on truckin’ back to that buffet for a fourth plate. Satiety can also be knocked out of whack by things like:

  • rare genetic disorders – about 5% of the obese population has some kind of genetic disorder that causes them to massivelyovereat (behaviour known as hyperphagia);
  • hormonal disruptions – for instance, disorders of pituitary hormone or insulin production; or simply decreases in normal hormone production with aging (aka the “menopause munchies”);
  • socio-environmental cues – for instance, in North America, we tend to eat until the plate is empty, no matter how big that plate (or platter) may be;
  • interpersonal social cues – we tend to match the pace and amount of our meal companions, so if other folks are eating more, we will too;
  • disrupted biological rhythms, such as sleep-wake cycles that don’t correspond to real daylight hours (for instance, working shift work or simply staying up too late with lots of artificial light);
  • other medications, drugs, or hormones – as many women on hormonal contraceptives, potheads, or folks on anti-depressant medication can attest;
  • substances in the food itself – which either deliver a lot of calories before our brains can tell our bodies to slow down, or encourage our bodies to eat more and more (for instance, high-fructose corn syrup); and
  • the food’s format – food in liquid form is less likely to satiate us, which is why it’s easy to put down 500-1500 calories with venti Frappucinos, jugs o’ Jamba Juice, or 64-ounce Super Big Gulps.

Into the mouths of babes

If you observe babies and young children, you’ll notice that most of them have perfect satiety mechanisms. When they’re done eating, they’re done. Try to get them to eat more and you’ll get a faceful of mashed peas spit at you. No matter how appealing that nipple, bowl of Cheerios, or amusingly-shaped pasta was five minutes ago, they couldn’t care less about it now. Generations of parents have coaxed, threatened, force-fed, and told stories about starving children elsewhere, to no avail. Kids know when it’s time to quit, and instead of being compelled by parental horror stories of famine, they usually suggest that the parents simply dump the rest of dinner into an envelope and mail it to those hungry African kids.

Though it’s frustrating as heck for parents, such behaviour is an elegant display of the satiety mechanism in action.

However, kids these days – doesn’t it feel wonderfully satisfying to complain about what “kids these days” are doing? – are finding it harder and harder to know when to quit.Even their iron-willed satiety signals find it difficult to cope with the onslaught of jumbled signals from processed foods. Such foods deliver a nerve-jangling blast of sugar, fake fats, and industrial chemicals such as artificial colours, flavours, and preservatives.

These foods are advertised relentlessly – almost literally jammed down kids’ (and parents’) throats. Yogurt tubes! Breakfast cereals! Fruit juices! Mini pizzas! When chef Jamie Oliver visited an American elementary schools as part of his Jamie’s Food Revolution television show, he discovered that school-age children did not know how to use knives and forks – they were used to consuming finger foods such as nuggets, hot dogs, hamburgers, and potato chips. Teachers literally had to show children how to use cutlery.

Not surprisingly, kids are getting fatter, faster.

The consequence of appetite: Obesity and overweight

In most industrialized countries, the prevalence of childhood obesity doubled or tripled between the early 1970s and late 1990s. In the United States, about 10% of children are now obese, but among some ethnic groups, up to half of children are obese.[1]

Even these statistics may not reflect the true picture: Official definitions of “overweight” and “obese” tend to under-count because of the stigma of obesity. As one research article notes, “Casual inspection would suggest that the actual rate of overweight in children is considerably higher than officially reported.”[2]

Table: Rates of childhood overweight and obesity (combined) in selected regions[3]

North America / 40%
Eastern Mediterranean WHO regions / 40%
Europe / 38%
Western Pacific / 27%
Southeast Asia / 22%

Data on kids’ snacking patterns shows that they’re snacking more, and snacking on more crap.

In the late 1970s, around 40% of adolescents between 12 and 17 ate no snacks at all during the day. In the mid-2000s, not snacking would make you a weirdo – over 80% of kids now snack, and one-quarter of those kids have three or more snacks a day (which reminds one of Homer Simpson’s triumphant exclamation that he’s invented a meal between breakfast and brunch).

Sugar and fat each make up about one-third of adolescents’ snack intake. Lean protein is low.Fibre is nonexistent. What these teenagers save in bowel movement time, they clearly make up with plastic package opening and straw slurping.

Vegetables barely squeak into 12% of consumption – which is bad enough, but now consider that the USDA’s definition of “vegetables” generously includes potato chips, French fries, ketchup (which is actually about straight-up glucose, aka sugar), salsa, and the sad little scraps of lettuce wilting on a hamburger or inside a taco. An American child could easily grow to adulthood never having consumed an actual dark green leafy thing.

Here are some of the top snack items for American adolescents[4]:

  • tortilla chips and corn chips/twists/puffs
  • cookies
  • pizza
  • white breads and rolls
  • crackers
  • potato chips
  • French fries
  • ketchup
  • apples, oranges, and bananas (apparently the one concession to actual food)
  • fruit juice and “fruit ades” (in other words, coloured, artificially flavoured sugar water)
  • milk (typically flavoured milks)
  • ice cream
  • chocolate
  • peanut butter
  • nuts (mainly in the form of candy)
  • hot dogs and deli meats
  • popcorn
  • soft drinks
  • candy
  • cake

Kids who snack take in as much as one-and-a-half times the calories as kids who don’t snack – mostly from sugars. A 12-year old girl who doesn’t snack consumes around 1500 calories a day. The same girl who snacks four times a day takes in about 2500. You can imagine what effect this excess intake has on her small, growing body.

For instance, girls are hitting puberty earlier these days, thanks to more body fat (which messes up both sex hormone production and insulin regulation), more food, and potentially environmental estrogens.Now, it’s not unusual for girls to start developing breasts around age 8 or 9; most menstruate around 11 or 12. In the 1800s, by comparison, an average girl got her period at 17. Early-onset puberty plus higher body fat is correlated to higher rates of breast cancer – especially if combined with the extra punch of contraceptive use, which many doctors, pharmaceutical companies, and worried parents encourage for emotionally immature girls in grown-up women’s bodies.[5]

Adults aren’t faring much better than kids when it comes to eating and health. The average person in an industrialized Western country eats over 3000 calories a day. Americans eat the most of anyone in the world – on average, 3826 calories a day.[6] That’s over 1000 calories a day more than the average global consumption of 2768 calories, and about 2000 calories a day more than the average Sub-Saharan African eats. (Folks in the Democratic Republic of the Congo are scraping by with an average intake of 1500 calories a day.)

(See file: Dietary Energy Consumption 2007-8.xls – revise chart as needed.)

Measuring overweight and obesity

Most Americans – about two-thirds – are now overweight. Canadians and Western Europeans aren’t far behind.[7]

In some regions of the United States, one in three people is obese.Among certain ethnic and income groups, the rate is much higher. Obesity goes up with poverty, and the poor white regions of the Southeastern US are particularly hard hit. Obesity is also more prevalent in some racialized groups, such as people of African, Latin American, Pacific Islander, and indigenous/Aboriginal descent. This is particularly true for migrants who have moved to North America and Western Europe, which tells us that it’s not just “genetics” that control body size and fatness.

More distressingly, the upper range of obesity is going up drastically.In other words, it’s not just that folks are getting gradually fatter – the proportion of folks who are seriously obese is going up fast.

One way to measure obesity is by using Body Mass Index (BMI), which is a measure of the relationship between weight and height.For the average person, a “healthy” BMI ranges between 19 and 24. In the last few decades, the number of people with BMIs over 40 has quadrupled. Obesity researchers now regularly see people with BMIs of 60 or 70.

To give you an idea of what this looks like:

If a person is… / They must weigh…
BMI of 20 / BMI of 30 / BMI of 40 / BMI of 50 / BMI of 60 / BMI of 70
6’ 0” / 150 lb / 220 lb / 295 / 369 / 443 lb / 517 lb
5’ 9” (1.75 m) / 204 lb / 275 lb / 339 lb / 407 lb / 475 lb
5’ 4” (1.63 m) / 175 lb / 233 / 292 lb / 350 lb / 408 lb

While there can be subtle variations within categories,

Many athletes complain that they get lumped in to the lower end of the BMI’s “overweight” category. Their extra weight comes from more muscle and denser bones, not fat.

It’s true that plenty of football players and pro wrestlers would end up officially “overweight” or even “obese” by BMI charts. A study of college athletes found that both male and female athletes were heavier but leaner than their nonathletic peers.[8] Women collegiate athletes, for instance, had an average BMI of nearly 28, compared to their nonathletic peers who had a BMI of 24 – but the athletic women had less body fat.Athlete’s bodies are bigger and heavier but leaner and denser.

This applies to many sports where strength, muscularity, and power are important.A 5’10”, 190 lb male NHL hockey player – well into the “overweight” BMI category with a score of 27 – might be nicknamed “Scrawny” by his teammates. A New Zealand All Blacks rugby player with Maori ancestry and BMI of 30 might be ashamed of his puny physique at 5’8” and 200 lb. Even in lean fighting shape, boxer Mike Tyson had a BMI of 31.

The problem, of course, is that BMI can’t measure what type of weight someone has – muscle, bone, water, fat, yesterday’s Hungarian goulash, etc. Thus, many folks have suggested that body fat percentage is a more accurate depiction of what we’re actually carrying around. This is a fair point. Five pounds of dense muscle is a lot leaner than five pounds of fluffy fat. Could we all be heavy because of muscle?

Nope. Evidence shows that our collective bodyfat percentage is high too.[9] Using dual-energy X-ray absorptiometry (DEXA), one of the most accurate methods of measuring body fat, researchers found that the average body fat for American men was 28.1%, while for women it was 40%. Normal body fat should be around 11-15% for men, and 21-25% for women.

By the way, many nonathletic people with “normal” or even “underweight” BMIs are actually overfat in terms of their percentage of body fat. In fitness circles, this combination of apparently “normal” body weight but a relatively high percentage of body fat – which signifies a lack of muscle and bone density – is known as “skinny fat”. “Skinny fat” isn’t healthy either. We need lean body mass – which comes from activity – to keep us strong, mobile, and well, especially as we age.

Even for athletes, muscle and daily workouts only go so far. A study of college football linemen, for instance, found that their average BMI was about 34, but their body fat was also well above average.[10]Similar data has been found for heavyweight strength athletes and sumo wrestlers.

Despite being active and fit, many heavier athletes have found that excess body fat and body weight catches up to them.Rates of chronic diseases such as cardiovascular disease, type 2 diabetes, and sleep apnea are – unfortunately – higher in fatter bodies, even if those fatter bodies are athletic. Past a certain point, the mechanics of excess weight (no matter what type) and the chemistry of adipose tissue outweigh (pardon the pun) the benefits of regular exercise and a high level of fitness.

When it comes to BMI, the rest of us non-Olympian schlubs have to accept the reality that BMI is, in fact, a very good measure of whether our body fat is in a healthy range. BMI as a general indicator of fatness is accurate for about 95% of the population.

The purpose of food, of course, is fuel. If our bodies need and use that fuel, then it goes to the right places.If we’re highly active and we eat a lot, our bodies stay lean and strong.

For instance, the 6’8” swimmer Michael Phelps’ combined training hours plus heat loss from cold water added up to an astonishing 12,000 calorie a day diet at the height of his training. Old Older Amish and Mennonite men do 10 hours a week of vigorous activity, 43 hours a week of moderate activity, and round that out with 12 hours a week of walking – a total of 65 hours a week spent moving. (Makes the “official” recommendations of “walk 30 minutes, 3 times a week” sound pretty pathetic, doesn’t it?)

However, if we eat a lot, but we aren’t active, then that fuel goes into storage. More storage and excess circulating fuel means big metabolic and mechanical problems.

Imagine you put together a lawnmower engine, wheels from a toy train, and the frame of a big ol’ Buick. Then you fill up the tank with some dirty diesel. How well will that car run? Not too well. Soon the structure will crack under the load, the engine won’t be strong enough to make the vehicle go, and the fuel will clog up the lines. You’ll be left with nothing more than a charming driveway ornament that you can display on cinder blocks for the aesthetic enjoyment of your neighbours. The same thing happens with a bigger body, supported by a smaller structure, with poor quality food in the tank.