The French Market Basket Study: How Much C15:0 Is In Our Grocery Products?

March 15, 2026

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Healthy Aging

Cheese & Butter, Please (with a caveat)

A research team in Rennes, France went to the grocery store, filled their baskets, and then measured how much C15:0 was in each of the food items. In addition to testing an impressive 15 different types of cheeses (this was France), they also measured C15:0 in other dairy products, as well as a variety of meats, fish & fish oils, seeds & seed oils, fruits & vegetables, and fermented products. Let’s see what they found (and what you may want in your grocery basket to optimize your C15:0 levels).

Sounds fun. Which foods had the most C15:0?

Not surprisingly, butter and cheese ruled over everything else in the grocery basket. Of the cheeses, the following had the highest C15:0 (measured as a % of total fatty acids):

Brie
Reblochon
Raclette
Morbier
Camembert

Now you know what to put on your next cheese plate. Interestingly, most of the full-fat dairy products – be it butter, yogurt, or cheese, had around 1.5% of C15:0, which is higher than what has been reported in dairy products outside of France. Full-fat dairy products in the U.S. typically have around 1.0% C15:0.

Proportion of fatty acids vs. absolute amounts in full-fat dairy foods

In this study, Ciesielski et al. measured both the % of C15:0 among all fatty acids and the actual concentration of C15:0 in food (reported as mg per 100 g product). While most full-fat dairy products had around 1.5% of C15:0 among all fatty acids, the wheat was truly separated from the chaff (or the butter from the yogurt) when they compared the actual amount of C15:0 per 100 grams of product.

In their study, they showed that butter had – by far – the highest amount of C15:0 per 100 grams. This was followed by cheese… and then yogurt (don’t even bother with the stirred yogurts).

Butter: 1,306 mg C15:0 per 100 g. This is approximately equal to a stick of butter.
Cheese: 322 mg C15:0 per 100 g. The winner was Morbier cheese, with 488 mg per 100g. This is about 1 to 1.5 cups of cheese.
Greek yogurt: 151 mg C15:0 per 100 g. This is about ½ cup of yogurt.
Stirred yogurt: Only 10 mg C15:0 per 100 g.

What else, besides full-fat dairy products, had C15:0?

Aside from full-fat dairy products, there were some types of fish and fish oils that had mentionable C15:0.

Among fish, most types – like cod, tuna, and haddock – only had 1 mg per 100 g of fish. A couple of winning fish types, however, included salmon (26 mg/100 g) and mackerel (53 mg/100 g). For reference, 100 g of fish is about a single serving size. When it came to fish oils, menhaden oil had an impressive 852 mg/100 g oil and mullet oil had 873 mg/100 g oil. Keep in mind, however, that 100 g of fish oil is equivalent to about a half cup of oil.

So, what are the optimal grocery basket items when it comes to C15:0?

Based on this study, here’s a sample grocery check list to boost your C15:0 (at least in France):

Butter from grass-fed cows
Morbier cheese (or most other high quality cheeses)
Greek yogurt
Fish (salmon or mackerel)

Yum. Alas, veggies, fruits, and tofu had negligible C15:0.

So, Where Do C15:0 Supplements Come In?

Studies have repeatedly shown that people need between 100 to 200 mg of added C15:0 per day to achieve healthy C15:0 levels (around 0.2% or 20 µM). So, if we can find foods that can deliver 100 to 200 mg of needed dietary C15:0 per day, then why supplement with C15:0?

Well, C15:0 supplementation is intended to achieve two objectives:

Achieve and maintain healthy C15:0 levels (> 0.2% or 20 µM): People who avoid full-fat dairy have lower C15:0 levels. Klein et al. showed that vegans had average C15:0 levels that were half of non-vegans (0.1%). C15:0 supplementation (100 to 200 mg/day) can help people who avoid dairy fat to maintain healthy C15:0 levels.

Optimize C15:0 levels (0.3-0.6%, or > 30 uM): For those of us who do indulge in full-fat dairy products, C15:0 supplementation can help people reach higher C15:0 levels that have been associated with:

Longevity. Manca et al. showed that Blue Zone Sardinians have C15:0 levels of 0.4-0.6%, which is 2 to 3 times higher than the average population.
Supported metabolic health. Schaefer et al. showed every 0.1% increase in C15:0 up to 0.6% resulted in 32% improvement in protected metabolic health.
Supported cardiovascular health. Shi et al. showed every 0.1% increase in C15:0 up to 0.6% resulted in up to 23% improvement in protected cardiovascular health.

It can be difficult to reliably maintain and achieve these optimal levels using dairy fat alone, keeping in mind that dairy fat also has much higher levels (about 40%) of pro-inflammatory even-chain saturated fats. In fact, both Schaefer et al. and Shi et al. showed that higher levels of total saturated fats and even-chain pro-inflammatory fats (like C16:0) in dairy fat are associated with a higher risk of developing type 2 diabetes and cardiovascular disease.

That’s where a pure C15:0 supplement comes in – to get the good C15:0 without the bad fats. With that, have a fantastic & (high quality) cheesy week, everyone!