In 2010, the federal low-income assistance program removed potatoes from the list of vegetables they would pay for. Later that year, Chris Voigt the executive director of the Washington State Potato Commission began a 2-month potato only diet in protest of this decision. He aimed to show that potatoes are a highly nutritious food and not just another starchy filler.
Results of the Potato Diet
His diet was roughly 10% fat, 10% protein, 80% carb. (He used some cooking oil for roasting). The results of this diet were completely unexpected:
- Lost 21 pounds
- LDL cholesterol decreased by 41%
- Triglycerides dropped by almost 50%
- Fasting glucose decreased by 10mg/dl
- His snoring stopped (as reported by his wife!)
He noted that potatoes gave him ‘a high sense of fullness after each meal’. After the third week, he had lost 12 pounds. This prompted Voigt to attempt to eat more calories, despite the fullness.
‘Bland Liquid Diet’ Experiment
The weight loss of the potato diet is not unprecedented. Previous research conducted in 1965 gave subjects unlimited access to a nutritional milk drink (Nutrament) (1). The subjects were instructed to have as much Nutrament as they wanted, but had no access to other foods. Lean subjects were able to maintain their bodyweight, whereas obese subjects experienced dramatic weight loss. One 400lb man continued the diet at home and lost 200lbs in 255 days. Remarkably,
‘ [he never] complained of hunger or gastrointestinal discomfort’.
His calorie intake spontaneously reduced when he started the liquid diet which continued throughout the experiment, much like Voigt on the potato diet. In contrast, the lean subjects’ calorie intake remained stable, and thus their weight was maintained.
Does Dieting Increase Hunger?
In 1976, researchers repeated this study with more subjects (2). Again, the subjects could have as much nutritional drink (Renutril) as they wanted, but no other foods. And again, the subjects lost weight on the diet. However, the researchers also tested the subjects’ palatability response to sugar-sweetened drinks (how much they liked sweets). Firstly, they infused glucose directly into their stomachs to give them a feeling of fullness. Secondly, they gave them sugar-sweetened drinks and tested how sweet they perceived them to be (how much they liked them).
After the Renutril diet, the subjects perceived the drinks to be as just sweet as they had before the diet (no change in their palatability response). However, subjects that had a varied and flavourful calorie-restricted diet, perceived the drinks to be sweeter than they did before the diet (the weight loss made them crave sweets more).
You can see the problem here: if you lose weight but become more hungry, it defeats the purpose. Eventually, your willpower will fail and your weight will rebound. The researchers also noted that the participants on the varied and flavourful diet:
‘had to continually fight off their hunger and would spend the night dreaming of food’
What Happens When Lab Rats Eat Cake?
A recent study gave rats either a standard chow, low fat, high fat, or cafeteria diet (3). The cafeteria diet included standard rat chow, plus 3 ‘human snacks’ rotated daily. The snacks included cookies, hot dogs, and even wedding cake!
The rats on the cafeteria diet increased their calorie consumption by 30% and gained almost doubled the weight of those on standard chow. Whereas, the high fat and low fat diets caused only moderate weight gain, compared to the standard chow. This study shows that rats love food variety and will happily eat themselves into obesity when presented with abundant junk food.
The Buffet Effect
Similar effects are seen in us. When presented with multiple food choices we unconsciously increase our calorie consumption. It is conveniently known as the buffet effect (4), as people tend to overeat at buffets.
In a 2009 experiment, Dutch researchers gave subjects a glass of chocolate milk (5). Afterwards, the subjects played a computer game to earn points for either, crisps or more chocolate milk. The subjects playing for crisps played harder and longer than those playing for chocolate milk (they wanted the crisps more). They also reported that the crisps tasted better than before the experiment, and the chocolate milk tasted worse. Overall, this study shows that after we have had one taste, we want a different one. We crave variety!
This phenomenon is called sensory-specific satiety, and is best summed up in this example: Remember the last time you were absolutely stuffed after a big meal, ‘full to bursting’ as my nan used to say, and then your host offers you dessert. All of a sudden your brain lights up, thinking: ‘mmm something sweet…I could probably squeeze it in’.
Part 1 Summary:
Why The Potato Diet Works, The 1st Reason – Food Variety
- Diets low in food variety, meaning they include a low number of foods, decrease calorie consumption in overweight people, and do so without the typical hunger associated with weight loss diets.
- Diets high in food variety promote overeating and lead to weight gain.