In my paleo nutrition seminar I use this study to illustrate how food affects hormones that in turn affect appetite.
In order to lose weight – you must eat less fuel. Fuel not used will get stored in your fat cells. There are two main ways to eat less (disregarding drugs and surgery):
- Have lots of willpower
- Eat a diet that you feel more sated on and naturally eat less food
Willpower does not usually last long, so the obvious choice is a diet whereby you eat less without feeling hungry.
This study illustrates clearly how and why eating more protein and less carbohydrates at each meal can literally halve the amount of food you want to eat.
But first, lets have a quick look at different macronutrients and their roles in your body:
Carbohydrates comprised of sugars and starches, and are built from mainly glucose and fructose molecules, sugars are 1- 2 molecules long and starches are many molecules long.
During digestion the links between the molecules are snipped apart by intestinal enzymes into single molecules. After crossing the gut barrier they go into the blood stream (your blood gets sweeter). Fructose gets taken up by the liver for processing, glucose on the other hand can readily be used by the cells for fuel.
Your pancreas senses the ‘sweetness’ of your blood and sends insulin out in order to get the sugar transferred out of the blood into cells where it can be ‘burnt’ for fuel. As a general rule, the more sugar in your blood – the more insulin you need to send out to remove it.
Protein on the other hand is made of strings of amino acids. During digestion peptidases (specific enzymes that snip apart an amino acid from its neighbour) break down these long strings.
The single amino acids then cross the gut barrier and are transported around the body to be used to make up proteins our body needs, like enzymes, muscle, bones, skin etc.
Protein like carbohydrate also triggers the release of insulin (something many people don’t realise) An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. Here are some high protein foods compared to white bread, showing insulin response:
However protein triggers the release of other hormones; in particular glucagon which increases satiety, and the release of glucose from the liver (Glucagon, Dietary Protein, and Low-Carbohydrate Diets)
How a higher protein, lower carb meal decreases your appetite compared to a high carb meal:
So lets have a look at this study which compares two different high carbohydrate meals (high and moderate glycemic index) with a lower carbohydrate meal (more protein and fat, less carbohydrates) and the effect of each on hormones, hunger and consequent food consumption.
The study (High Glycemic Index Foods, Overeating, and Obesity):
- 12 obese teenage boys, crossover study, 3 separate 24 hour admissions to hospital, 1 -2 weeks washout periods in between
- 3 different meals were evaluated, high GI, moderate GI and low GI, one on each admission. (Note: all meals had identical calories)
- The boys ate the same meal for breakfast and lunch and were allowed to eat as much or little as they liked for the rest of the day. The exact amount consumed was measured.
- A number of measurements were taken – blood sugar, insulin, glucagon, epinephrine, hunger ratings.
Here are the actual meals, two meals are typical high carbohydrate / grain /dairy – the type of meal that would be considered a healthy breakfast by just about all mainstream dietitians – each has a different glycemic index, one is slow cooking oats, the other instant oats. The other meal contains less (and non grain) carbohydrates, and more protein and fat – in a Zone diet macronutrient ratio.
|Foods||55 g Whole egg||63.9 g Steel-cut oats *||60.9 g Instant oatmeal *|
|45 g Egg white||160 g 2% Milk||160 g 2% Milk**|
|40 g Low-fat cheese||15 g Half & Half cream||15 g Half & Half cream|
|200 g Spinach||16.0 g Fructose||19.0 g Dextrose|
|30 g Tomato||0.0 g Saccharine||0.2 g Saccharine|
|185 g Grapefruit||397 g Water||397 g Water|
|115 g Apple slices|
|% Energy from carbohydrate||40||64||64|
|% Energy from protein||30||16||16|
|% Energy from fat||30||20||20|
|Energy density (kJ/g)||2.46||2.52||2.52|
The first graphs show the elevation of blood glucose after the different meals; as you would expect, the two higher carb meals (circle, square) had a much higher glucose elevation than the moderate carb meal. Insulin response mirrors the carbohydrate content of the meals.
Compare the two high carb meals: The quick cook oats had the greatest increase in blood sugar, and around the 3.5 hour mark – it continues to drop – below the fasting level. The range shows all boys responded this way. When your blood sugar goes low, your body responds by elevating the stress hormone epinephrine or adrenaline. This is shown clearly on the lower graph. There is a large increase in epinephrine in the high GI meal compared to the other meals. Adrenaline is the flight / fight hormone, and is released to increase blood glucose via glycogenolysis. The moderate GI meal surprisingly had almost no adrenaline response, and the high protein, low carb meal very minimal. (Does this mean that carbohydrates – if they are very slow release are beneficial? Or did the epineprine rise as glucagon levels fall around the 4 hour mark?)
Hormonal and metabolic changes after test breakfasts. Plot symbols: square, high-GI meal; circle, medium-GI meal; triangle, low-GI meal.
Glucagon is released by the pancreas in response to protein, it has an appetite suppressant effect, as well it elevates the amount of glucose in the blood by promoting gluconeogenesis and glycogenolysis.
In the graph below you’ll note that glucagon is suppressed by the high carbohydrate meals and increased in the higher protein meal for around 4 hours post meal.
So the effects of these foods on hormones is interesting – but what about subsequent hunger, and food consumption?
The boys had the same meal for breakfast and lunch, then for the rest of day they could eat as much as they wanted from the food provided. They also gave a hunger rating every hour for the 5 hours following breakfast.
This graph shows the difference in hunger following each meal – the hunger experienced was significantly greater on the high carb meals:
Change in hunger after test breakfasts. Hunger is determined by a 10-cm analog scale.
Food consumption for the rest of the day
When the boys were allowed to consume what ever they wanted following lunch, the first thing to note is that some boys got hungry and started to eat within 1 hour of consuming the quick cook oats. The boys who ate the higher protein lower carb meal did not start to eat until the 3 hour mark. By the end of the day the difference is dramatic – those who ate the high refined carb (quick cook oats) meals ate nearly double the amount of food compared to those that ate the higher protein lower carb meal.
Cumulative food intake after test lunches. Food intake is quantitated as total energy consumed, expressed in megajoules, and normalized to a predicted RMR of 8.4 mJ (2000 kcal).
And in another study just released – having a high protein breakfast, compared with a high carb, or no breakfast, helped women eat less during the rest of the day:
Take home points:
If you want to control your hunger – eat protein at every meal, start your day with protein at breakfast – you will elevate the hormone glucagon which increases satiety. (We eat meals the wrong way round – try eating dinner for breakfast) And no yoghurt is not that high in protein – try protein dense food like eggs or meat, use this chart and get a minimum of 20 grams, ideally 30. Protein amount in eggs, seafood, meat and dairy.
Eat whole vegetable and fruit carbohydrates rather than grains (this article describes further benefits of vegetable starches over grain starch: Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity)
Add a little fat to your meal, it slows down the digestion of carbohydrates and also helps satiety.
Think of every meal as controlling blood glucose and satiety hormones for the following 4 – 6 hours, and experiment with your meals to find ones that manage your hunger best.
For some it means more fat and less carbohydrates – particularly if you are insulin resistant. In this case stick to non starch carbohydrates and add more healthy fat like avocado to your meal along with the protein. Watch this excellent video from NZ scientist Dr Grant Schofield on this topic here: