“Fries are not a health food” is not breaking news, but how often can you get away with them before it starts impacting health outcomes?

Researchers (Dr. Seyed Mousavi et al.) investigated the effects of fries, various kinds of non-fried potatoes, and white vs whole grains, on diabetes risk.

This was done over the course of three US cohort studies involving a total of a total of 205,107 participants, mostly women, whose diet and health outcomes were followed for 4 decades. Of these participants, 22,299 developed type 2 diabetes.

Here’s what they found:

❝After adjustment for updated body mass index and other diabetes related risk factors, higher intakes of total potatoes and French fries were associated with increased risk of T2D.

For every increment of three servings weekly of total potato, the rate for T2D increased by 5% (hazard ratio 1.05, 95% confidence interval (CI) 1.02 to 1.08) and for every increment of three servings weekly of French fries the rate increased by 20% (1.20, 1.12 to 1.28). Intake of combined baked, boiled, or mashed potatoes was not significantly associated with T2D risk (pooled hazard ratio 1.01, 95% CI 0.98 to 1.05).

In substitution analyses, replacing three servings weekly of potatoes with whole grains was estimated to lower T2D rates by 8% (95% CI 5% to 11%) for total potatoes, 4% (1% to 8%) for baked, boiled, or mashed potatoes, and 19% (14% to 25%) for French fries. In contrast, replacing total potatoes or baked, boiled, or mashed potatoes with white rice was associated with an increased risk of T2D.

In a meta-analysis of 13 cohorts (587 081 participants and 43 471 diagnoses of T2D), the pooled hazard ratio for risk of T2D with each increment of three servings weekly of total potato was 1.03 (95% CI 1.02 to 1.05) and of fried potatoes was 1.16 (1.09 to 1.23). In substitution meta-analyses, replacing three servings weekly of total, non-fried, and fried potatoes with whole grains was estimated to lower the risk of T2D by 7% (95% CI 5% to 9%), 5% (3% to 7%), and 17% (12% to 22%), respectively.❞

That’s a lot of numbers, so let’s break it down, translate it from sciencese, and look at some of the key points.

In order, we have, for the emprical data:

• Every extra three servings of total potatoes per week increased risk by 5%
• Every extra three servings of French fries per week increased risk by 20%
• Baked, boiled, or mashed potatoes gave no significant change in risk
• Replacing three weekly servings of total potatoes with whole grains lowered risk by 8%
• Replacing baked, boiled, or mashed potatoes with whole grains lowered risk by 4%
• Replacing French fries with whole grains lowered risk by 19%
• Replacing total potatoes or baked, boiled, or mashed potatoes with white rice increased risk by 15%*

And now for the meta-analysis** numbers:

• Every extra three servings of total potatoes per week increased risk by 3%
• Every extra three servings of fried potatoes per week increased risk by 16%
• Replacing total potatoes with whole grains lowered risk by 7%
• Replacing non-fried potatoes with whole grains lowered risk by 5%
• Replacing fried potatoes with whole grains lowered risk by 17%

*This figure wasn’t in the abstract we quoted above, but we found it in the full substitutions table lower down in the paper, where it’s expressed as a Hazard Ratio of 1.15, which equates to a 15% increase in risk.

**A meta-analysis can be thought of as an “imaginary experiment” performed by collated existing data from other studies, running it through statistical models, and seeing what comes out. As you can see, the resultant numbers are slightly different, but the associations remain the same (i.e. the same additions/substitutions still give approximately the same relative increase/decrease in risk), which means the meta-analysis also supports the conclusions drawn from the empirical data.

On which note, the full paper itself can be found here: Total and specific potato intake and risk of type 2 diabetes: results from three US cohort studies and a substitution meta-analysis of prospective cohorts

That’s a lot of information; what’s most important?

In few words:

• Whole grains are the best
• Non-fried potatoes are ok
• White grains are bad
• Fried potatoes are the worst

Thus, substituting between those four categories will yield changes in risk proportional to how far apart they are from each other on that list.

Furthermore, to answer the question posed in our introduction today (how often can one eat fries before it starts impacting health outcomes), the honest answer is: never, technically.

See for example: Is Fast Food Really All That Bad? ← we realize that fries do not necessarily have to be fast food, but they share the nutritional profile being examined there.

And while “one bad meal” will not impact long-term health, it will have an immediate negative impact on short-term health, due to its gut-disrupting activity. If it really was just a one-off meal, an otherwise healthy gut will bounce back just fine, but it’s another argument for the case of “the negative health effects do start immediately”.

However, the dose does make the poison, and in this case, increments of 3 portions per week increased risk by 20%. We can say, therefore, that each portion per week increases the risk by 6.6%, and this risk is cumulative.

On which note: what is a portion?

• A portion is not: “however much you eat at once”
• A portion is: “a 4–6 oz serving”

So, if you have twice that at a sitting, that’s two portions. Thrice that at a sitting, and that’s the weekly 3 portions that increase the risk by 20%, already, in one day, and if you have more in the rest of the week, it will continue to add to the risk cumulatively.

If you’d like to dial down the portion sizes while simultaneously enjoying what you eat more, there are two useful approaches you might want to consider (you can do both if you want; there’s no conflict between them, and in fact, they can go quite well together):

• Some Surprising Truths About Hunger And Satiety
• Mindful Eating: How To Get More Out Of What’s On Your Plate

Want to learn more?

Check out:

Carb-Strong or Carb-Wrong?

Take care!