In Part 1 I explained why the low food variety of the potato diet decreases hunger and causes one to unconsciously eat less. Now, in part 2 I will explain how the low palatability of the potato diet also decreases calorie intake.
How Filling Are Potatoes?
In 1995, Dr. Susanna Holt and her colleagues at the University of Sydney devised an experiment to find out how filling everyday foods are (1). In short, they gave subjects everyday foods to eat and asked them how full they felt, per 240 calories of each food.
Protein, fibre and water content increased satiety; whereas palatability, fat and sugar content decreased satiety. Calorie density was the strongest predictor of satiety. So, calorie dense foods like cake and chocolate bars left people feeling hungry. Whereas, calorie sparse foods such as porridge and potatoes filled people up. In fact, potatoes were the most filling food. They were 7x more filling than the least satiating food: croissants.
*white bread = 100%, used as a reference point
After the food tests, the researchers gave the subjects a breakfast buffet and recorded how much they ate. The more satiating the original food, the less they ate at the buffet. Therein lies the second secret of the potato diet. Potatoes are very filling and calorie sparse, therefore it is difficult to eat a large number of calories of them. Chris Voigt experienced difficulty eating enough to maintain his weight, on his 2-month potato diet. This is a testament to their filling effects.
Problems with the Willpower Theory of Obesity
To understand why the potato diet worked, we must understand how weight loss works in general. We all know eating more calories increases weight gain, but the real question is: what makes us eat more? The common and naive explanation for this is self-control. It goes something like this: food intake is all a matter of self-control. Those who have good self-control limit their food intake and are lean. Those who don’t, eat to excess and suffer the consequences.
However, there are several problems with this theory:
- Obesity rates have tripled since 1975 (2). Has self-control has also decreased by 3 fold? It seems unlikely.
- Willpower has been found to be a finite resource that is easily spent (3). Reliance solely on willpower as a dietary strategy would be unsuccessful, for anyone.
- In the 1960s, Ethan Sims fed US prisoners 10,000 calories a day to sustain a 25% weight gain (4). After the study, most had no appetite and slimmed down to their original weights. This suggests weight and appetite are unconsciously controlled, rather than a matter of conscious effort.
Problems with the Carbohydrate Theory of Obesity
The potato diet almost single-handedly destroys the insulin theory of obesity i.e. carbs make you gain weight. Potatoes are 93% carbohydrate and are a high GI food, and therefore the potato diet would be a surefire way to gain weight. However, Voigt and others have experienced the exact opposite of this.
The Current Theory of Obesity: Food Reward
Nowadays, the most prevalent theory of obesity is the food reward hypothesis. The theory states that: foods that are highly rewarding and palatable override our physiological mechanisms of satiety and cause us to overeat (5).
Our bodies evolved in an environment where calories were scarce and we spent most of our lives trying to get them. Therefore, we have evolved a drive to push us to obtain food. We feel pleasure when eating foods, and hunger when not. This reward system urges us to seek food. Eating food releases dopamine, our brains’ reward neurotransmitter, the more calorie dense the food, the more dopamine is released (6). We obtain food for the neurochemical reward, and this behaviour ensures our survival.
When we eat modern highly palatable foods it overrides our bodies’ normal signals of satiety and informs us calories are abundant in this environment. To ensure our survival, our bodies encourage us to overeat.
Take for example the Ache tribe, in one sitting they will eat either 5lbs meat, 20-30 oranges or 1.5L honey (7). This shows how we will naturally overeat in the presence of abundant calories and palatable foods like honey.
Modern vs. Traditional Diets
The diet of hunter-gatherers, and then later agriculturalists would have been far less palatable than today’s, consisting mainly of only a few staples. The Hadza, a modern day hunter-gatherer tribe in Tanazia, derive most of their calorie intake from 5 foods: honey, meat, berries, baobab fruit and tubers (8). The potato diet takes this simplicity to the extreme and helps explain its success.
It is only after the industrial revolution and the second agricultural revolution 200 years ago that many of us were not required to farm our own food. Modern processed foods became widely available in the 1950s, and have increased in popularity since.
We now find ourselves in the world’s biggest sweet store. There is an abundance of highly palatable and calorie-dense foods, with never-ending variety. Moreover, we do not have to work for our food, but simply drive to the nearest shop.
Evidence for the Food Reward Theory of Obesity
As you can see from the 1st graph, our daily energy intake has increased by 218 calories, since 1975 (9). The 2nd graph shows the dramatic increase in processed foods and decrease in whole foods since the 1950s (10). Thus, taking both graphs together we can show the rise in calories to be a result of increased processed food consumption.
Processed foods are highly palatable and are consciously designed to be, by the food industry. The food industry has a vested financial interest in making sure you consume as much as their products as possible. These foods override your satiety signals and encourage you to overeat.
What Makes a Food Palatable?
- Meatness (umami)
- Multiple flavours
- Calorie Density
- Water Content
- Calorie Sparse
Palatability Example: Potatoes
Take for example a boiled potato, it has plenty of fibre and water, and the calorie density is low, so it has low palatability. However, if we decrease the fibre by peeling, reduce the water by cooking, add fat and flavour by deep frying, and season with salt. We now have a highly palatable food: french fries (or chips). This process concentrates the calories, increasing the calorie density. The higher the palatability is, the less satiating the food is, therefore we need to eat more calories to feel full.
Simple Food Tastes Great!
You might now be in despair, thinking the only way to lose weight is on a bland diet. That is only half true. A study done in 1982 showed that subjects who ate a low sodium diet ended up disliking the taste of high salt foods and prefered ones with low salt (11). Moreover, a recent study showed that people who ate a low sugar diet became more sensitive to sweet tastes (12).
This shows that our taste buds can adjust to lower palatable foods. The studies were a few months long, so you can except your taste buds to adjust in a similar time frame. I can also attest to this effect, based on my own personal experience. Simple foods like steamed vegetables taste great, whereas before they tasted bland. Also, I can no longer enjoy very sweet foods such as Ben and Jerry’s ice cream, which is now almost inedible to me.
Dopamine receptors downregulate when they are exposed to large amounts of dopamine frequently. When the dopamine receptors are less active it takes more dopamine to get the same feel-good state. Therefore, if you are constantly eating highly palatable foods and releasing large amounts of dopamine, the receptors will become less sensitive. Meaning, you will require more highly palatable foods to get the same neurochemical satisfaction (13).
However, if you decrease the amount of dopamine you release (stop eating highly palatable foods), your receptors will upregulate, and then a smaller amount of dopamine will provide you with the same satisfaction. Meaning, less palatable foods will become more satisfying and enjoyable to eat. This effect may take a few months to fully kick in. The trick is not to go back to the junk food whilst adjusting.
Part 2 Summary:
- Our brains are wired to seek out palatable and calorific foods.
- The diets of our ancestors were based on simple foods, and our satiety responses were designed for these basic foods.
- Modern processed foods are highly palatable and calorie dense, which overrides our normal satiety signals and causes us to overeat.
- The more palatable a food, the less filling it is. Therefore, you need to eat more calories to feel full.
- Your taste buds adjust to simple foods, and they become as enjoyable to eat, as junk food.
Note: The point of this post and part 1 is not to recommend the potato diet, but to understand the principles which make it work and then apply them to weight loss.