You can watch this guy cover the same ground in lecture format. Several versions have been released over time. My favorite is an early one in which he includes a bit of the biochemistry. Don’t let that put you off – biochemistry is beautiful in outline tedious in detail. Just ignore the detail.
Broadly speaking plants get their energy by converting sunshine into sugar. Animals have to eat. Either way the currency of energy is glucose. C₆H₁₂O₆. Burning it consumes oxygen and yields carbon dioxide, water and releases the means to cause muscle to contract, brains to think and all the other processes living things have to carry out.
And a lot of those processes are aimed at keeping the interior environment of the organism in a fairly constant state consistent with continued survival, a process called homeostasis. When a meal is ingested a very complex chain of events follows. To coordinate it all cells and organs need to communicate with each other and they do this by a number of means.
Think of a thermostat , a thermometer and a heater. At a certain temperature the the thermometer triggers a message that turns on the heater. The temperature rises. When it reaches another temperature the thermometer triggers another message that turns the heater off. The temperature stays within set limits and we have a simple example of a negative feed back loop.
Now magnify that many times over. The messages can travel by nerves or by chemicals. Some chemicals may not go far, some enter the circulation and have their effect remotely. Think about something delicious and you will prepare the pleasure centres of your brain for impending enjoyment and your salivary glands will get to work. This will intensify as you see it or smell it. Start chewing and your taste buds will bring more information to your brain’s attention. When your stomach begins to fill the distention will trigger an impulse via the vagus nerve to tell the brain to think about stopping eating. The gut gets to work on digestion. Nutrients are absorbed, transported, processed and stored. All this has to happen without pushing the internal environment out of kilter. And feedback loops are working at every step of the way.
The number of chemical messengers is staggering. For a glimpse at how complex it all is try this <Paper> even if only to see how much I’ve simplified what comes next.
Among the chemicals at work there are some internet stars, Ghrelin, Leptin and Insulin among them.
When your tummy grumbles think of Ghrelin. It is mainly secreted by the stomach and acts mainly on the hypothalamus. Levels are high when fasting and as meal times approach. Injection of Ghrelin will stimulate the desire to eat. After your successful weight loss diet Ghrelin will help you put the weight back on.
Leptin on the other hand will help you stay the same weight. Leptin comes from happy fat cells, levels rise in obesity and fall during weight loss. If it’s allowed to do its job it triggers a complex series of events in the brain which suppress appetite.
Evolution came up with a system that prompted us to eat when energy was needed and stop when we’d eaten enough. It also had to permit storage of excess energy when available against the times when food was scarce. We store excess glucose by turning it into fat, we have no similar mechanism for storing excess protein. The diet that evolution got to work on for almost all of human existence was a hunter gatherer diet. Tubers, meat, fat, fruit in season and maybe honey once in a blue moon.
The agricultural revolution began about 12,000 years ago. Grains became much more prominent. Evolution continued to work and has made it possible for some of us to consume milk after infancy. Has it brought us to a point where we are as well in tune with our diet as we were before?
The industrial diet has seen sugar intake rise from negligible amounts to a point where we are eating almost our own weight of sugar a year. Our weight at the beginning of the year that is.
Processed food now consumes 22.9% of our food expenditure, more than all other categories with meat in second place.
Westerners are eating about a third more calories than we actually need.
This dietary change is recent. Evolution has had no time to hand a Darwin award to the unfit but it’s working on it. We are getting fat and we are getting sick (not necessarily both, some obese people are metabolically well).
We don’t like being fat, just look at the shelves in the book shop. We diet, we join the gym … and we fail. So if it’s not a hedonistic plunge into gluttony and sloth why are we in the midst of an epidemic of obesity, diabetes type 2, metabolic syndrome, cardiovascular disease, cancer and dementia?
Well obesity and diabetes are obviously related to what we put in our mouths. Could the culprit be the newly abundant refined carbohydrates we’ve added to our diet?
Sucrose is a molecule of glucose joined to a molecule of fructose. These are quickly split asunder in the gut and absorbed individually. Glucose can be metabolised by virtually every cell in the body. Fructose can only be metabolised in the liver. Glucose goes every which way, only a fraction ends up in the liver. All the fructose goes to the liver. Fructose is about twice as sweet as glucose.
In the liver spare glucose is stored as glycogen. Good stuff, ask any endurance athlete. Excess is exported for storage as fat. Bad stuff ask any endurance athlete. None of the fructose ends up as glycogen, if it’s not used immediately for energy it goes to fat. If the liver is swamped the fat doesn’t get exported fast enough. Now we have a fatty liver.
Fructose was present in our hunter gatherer diet. Our ancestors enjoyed fruit, it’s delicious and a rich source of energy. It was seasonal and in limited quantities, gorge on it now, store the energy for the lean times. It made good evolutionary sense. That was then, now we have fructose on demand, our livers are swimming in the stuff, every day. Not only in fruit, its in almost everything that comes in a packet or a bottle.
When sugars hit the bloodstream the pancreas sends out insulin. The job of insulin is to pack glucose away into cells. Muscle cells grab what they need and store it as glycogen. This will be used as fuel during muscle activity. There is no mechanism for getting it out again. Fat cells will store it as fat. This can be re-exported when needed but not while insulin levels are high. Other cells take what they need for energy.
The Leptin level is rising, blood glucose and insulin are coming down. The pleasure centres of the brain are buzzing. All is well with the world.
Soon the blood glucose is getting low again. We can leave it to our physiology to sort that out or we can have another soft drink, gee that was good. All too often our pleasure centres opt for the quick fix.
Over the years of repeated bursts of sugar our cells begin to be less responsive to insulin. The pancreas responds by making more. Glucose levels remain normal but fasting insulin levels are raised. This means that fat cells cannot export glucose. Raised insulin prevents Leptin delivering its message to the brain. Hunger now has the upper hand, fat utilisation has ceased, weight is going up.
A few years later the poor old pancreas will not be able to keep up. Insulin output drops, blood glucose soars. This is now type 2 Diabetes.
By now the fat is surrounding your organs, your arteries are narrowing and stiffening. Your blood pressure is rising along with the risk of a heart attack or stroke.
Diabetes Australia recommends following the Australian Dietary Guidelines but eating little and often. Apart from some chocolate and the odd icecream isn’t that how we got into this mess? In time you will have to start injecting Insulin …
When insulin is required, it is important to understand that this is just the natural progression of the condition.
So just surrender.