I came across this Yahoo Finance article describing the viewpoint of longevity scientist Valter Longo that consumption of the “poisonous 5 P’s”—pizza, pasta, protein, potatoes, and pane (bread)—in Italy’s youth is a threat to their possibility of having a healthy lifespan. Specifically, Longo claims that regularly eating these foods is one of the reasons for the country’s rising obesity rates. Before cutting these delicacies out of our lives, though let’s discuss the research investigating whether or not consumption of the poisonous 5 P’s makes us gain weight.
The Biological Process Behind why experts think the Poisonous 5 P’s might make us gain weight
The thought-process behind why pizza, pasta, potatoes and pane (bread) are thought to be “fattening” mostly stems from their relatively high glycemic indexes (GI). When we eat high-GI foods, our blood sugar levels rise very high, very fast. Sensing this increase in blood sugar, our pancreas releases a rush of the hormone insulin. Insulin then instructs our adipocytes (fat cells) to: 1) uptake glucose from the blood and 2) make and store triglycerides (fat)1. I won’t get into too much detail here, but just understand that it is thought that habitually eating high-GI foods encourages our fat cells to make and store fat regularly—fat that will be bound up and thus not “burned” by muscle cells as energy.
As for the third “P”, protein, there is a twofold reason why it may be reasoned that high protein intake is a contributor to our obesity epidemic. Firstly, our bodies can convert protein from our diets into glucose through a process called gluconeogenesis; dietary protein promotes insulin secretion2. Secondly, most people, at least in America and many other wealthy nations, meet or exceed our protein requirements as recommended by nutrition experts3. It may be reasoned that our excessive protein intake is resulting in an overproduction of insulin. Of course, elevated insulin levels would ultimately lead to fat storage.
Do the poisonous 5 P’s actually make us fatter?
Now that we have a basic understanding of why pizza, pasta, protein, potatoes and pane (bread) may possibly make us fatter on a biological level, let’s look at the evidence to see if the hypothesized effects of these foods are true in real life. Here are the findings of some studies on the associations between each of these five foods and weight status:
1. Pizza
All of the studies I could find on the association of pizza consumption and weight status were focused on children, not on adults. (Maybe this has something to do with the fact that a higher percentage of adolescents eat pizza than adults4). In general, these studies report that, on the days they eat pizza, children eat more calories, sodium, and/or saturated fat than on the days that they don’t eat pizza5,6.
As an aside, yes, kids eat more calories on the days that pizza is on the menu, but as I’ve referenced in above, overfeeding on calories doesn’t necessarily translate to weight gain—what matters is the ways different types of foods (based on things like Glycemic Index) are digested in our bodies7. Even though, for kids, pizza day means higher calorie intake, this doesn’t necessarily mean that kids who regularly eat pizza are more likely to be overweight than kids who don’t.
BUT interestingly, a study investigating the influence of fast food consumption on the weight status of students in Iran found that, compared with students who reported eating other kinds of fast food within the past month, students who reported eating pizza in the past month were especially more likely to be overweight. The authors explain, “Sandwich consumption was associated with obesity/overweight based on BMI to 35%, fried chicken to 40%, and pizza more than 80%.”8
2. Pasta
A 2023 review of thirty-eight different studies investigating the association between pasta consumption and weight reports that in general, observational studies “report no association or an inverse association of pasta intake with body weight…”9 From the research at large, it seems that pasta-eaters are NOT more likely to be overweight than non-pasta eaters; some evidence suggests that pasta-eaters may weigh even LESS than non-pasta eaters.
Take note that this is a general finding. Not all of the 38 studies investigating this pasta-weight relationship came to the same conclusions. The authors of the review note that three of these observational studies found a positive association between pasta consumption and body weight change (the research subjects who eat pasta were more likely to gain weight than those who didn’t). However, the significant majority of the observational studies found no association or an inverse association between the two. Pasta lovers, one and all, shout for joy!
3. Protein
“Protein” seems like a pretty broad category of food, doesn’t it? Well, an “umbrella” study took a broad approach to the topic of dietary protein intake and body weight, fat mass, and waist circumference. These researchers found that in studies where participants did not restrict calories, a high-protein diet had no effect on body weight, fat mass or waist circumference. Meanwhile, in studies where participants restricted calories, a high-protein diet seemed to decrease body weight. The authors note that there was not enough evidence to make a decision on whether protein type (plant vs animal) has any effect10.
Another review similarly reports that even when we overeat, “the consumption of a high protein diet may not result in a gain in body weight” and that “dietary protein appears to have a protective effect against fat gain during times of energy surplus”11.
4. Potato
As one of the starchiest, highest GI foods, there’s a general consensus that in order to lose weight, potatoes should not be a regular part of the diet. One study put this long-standing belief to the test. Ninety overweight men and women were randomly assigned to one of 3 diets: 1) high GI diet, 2) low-GI diet, and 3) no GI provision diet. What’s important for our purposes is that all participants were instructed to consume 5-7 servings of potatoes per week. Regardless which one of the 3 diets the participants followed, all three diets caused the participants to lose about the same amount of weight—potato intake did NOT cause weight gain12.
Another study looked at whether the method of preparation matters for potatoes and weight. The investigators report that for women, but not for men, fried potato consumption is directly related to having a higher BMI, and also higher blood pressure. Other methods of potato preparation (boiled, mashed, baked…) have no effect on BMI in neither men nor women13.
Lastly, one study compared the effects of potatoes (a “natural” high-GI food) with refined grains (a “man-made” high-GI food) on weight and fasting blood glucose levels. In short researchers split their participants into one of 2 groups for four weeks: 1) eat a side-dish of potatoes daily or 2) eat a side-dish of refined grains daily. At the end of the study, there was no difference in weight or fasting blood glucose levels between the two groups. Compared with daily intake of refined grains, daily intake of potatoes does not effect biomarkers of weight and also is associated with better overall diet quality14.
5. Pane (Bread)
Speaking of refined grains, we’re on the last of our poisonous 5 P’s—bread—urghhh “Pane“. I think bread is by far the most villainized of the five (remember those WeightWatchers commercials where Oprah shocked the world by exclaiming that we can lose weight while still eating our beloved bread?). Anyways, the research somewhat supports her claims.
One study looked at the effects of changes in bread consumption over time in people at risk for cardiovascular disease. The investigators assessed the research participant’s diets once a year over four years, looking at how much their bread intake changed over the years. It turns out that participants who had the highest increases in white bread consumption over the four years gained significantly more weight and waist circumference than participants who had the lowest increase in white bread consumption15.
A group of researchers reviewed the summaries 38 studies that investigated the associations between bread intake with abdominal fat and ponderal status (this is similar to BMI). Their findings on whole-grain bread are good: diets that include whole-grain bread do not seem to promote weight gain and may help with ponderal status (BMI). Their findings on diets that include refined bread are mixed, as “the majority of cross-sectional studies indicate beneficial effects, while most of the well-designed cohort studies demonstrate a possible relationship with excess abdominal fat”16.
Conclusions
All-in-all, I think the evidence tells us the following: 1) we might want to limit our pizza intake, 2) enjoy pasta night, 3) protein is the way to go especially if you’re going to overeat, 4) stay away from french fries and chips, but enjoy all other kinds of potatoes, and 5) whole grain bread is fine, eat white bread in moderation.
- https://diabetesjournals.org/diabetes/article/66/4/815/16020/Role-of-Adipose-Tissue-Insulin-Resistance-in-the ↩︎
- https://pubmed.ncbi.nlm.nih.gov/24986822/#:~:text=Dietary%20proteins%20have%20an%20insulinotropic,glucose%20clearance%20from%20the%20blood. ↩︎
- https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/are-you-getting-too-much-protein#:~:text=Contrary%20to%20all%20the%20hype,from%20meat%2C%20poultry%20and%20eggs. ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4085193/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4306796/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC5051708/#sec012 ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC5786199/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6196377/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10300797/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10799103/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC5786199/#sec7 ↩︎
- https://pubmed.ncbi.nlm.nih.gov/25302575/#:~:text=Potato%20intake%20did%20not%20cause,nature%20of%20changing%20dietary%20patterns. ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC8219046/ ↩︎
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7282869/ ↩︎
- https://pubmed.ncbi.nlm.nih.gov/23199451/#:~:text=The%20present%20results%20suggest%20that,in%20weight%20and%20abdominal%20fat. ↩︎
- https://academic.oup.com/nutritionreviews/article-abstract/70/4/218/1937101?redirectedFrom=fulltext&login=false ↩︎