A friend of mine at work brought a recent study to my attention recently published in the Journal Diabetes Care.
The investigators of this article obviously think so, titling it “Saturated Fat is More Metabolically Harmful for the Human Liver than Unsaturated Fat .”
And old idea, with newer explanations
The idea these investigators have is that that saturated fat contributes to hepatic ceramide accumulation and endotoxemia. Endotoxemia being the passage of bacterial particles from your intestinal tract into your blood stream. These particles cause your immune system to pull fire alarms and cause lots of inflammation, contributing to obesity and diabetes. Many proponents of this theory believe dietary fat, particularly saturated fat, is a major contributor. You can read more about this concept here  and here .
The ceramide synthesis contributes to insulin resistance, triglyceride accumulation in the liver, and endotoxemia furthers this ceramide mediated process.
What happened in the study
The investigators subjected 3 groups of men and women to 3 different means of overfeeding by 1000 calories. One group consumed 1000 calories from saturated fat (SAT), another from unsaturated fat (UNSAT), and another from carbohydrate (CARB) in the form of simple sugars. Overfeeding took place in a real world setting for three weeks and compliance was assessed with 3 day dietary diaries and lipid content of lipoprotein particles before and after the study.
Changes in liver fat content, insulin sensitivity, lipoprotein lipid content and adipose gene expression were tracked at baseline and after the study. All the markers favored overfeeding in the unsaturated fat group, with the saturated fat group performing the most poorly.
Hold on a second…
Whenever I read about dietary interventions, I always like to see what the precise composition of the diets are. What’s interesting to note here:
630 calories of the extra burden is from oil in the SAT group, mostly from coconut oil and butter.
The remaining calories in the SAT group came from blue cheese.
504 calories of that burden in the UNSAT group came from oil, mostly from olive oil and then butter.
The remaining calories in the UNSAT group came from pecans and pesto.
This might be important to note because first, oil is pretty much empty calories. Butter has a small amount of fat soluble nutrients and minerals. Second the remaining contributors to calories impact the diet in other ways.
The nutrient contribution across dietary approaches is variable, with the SAT dietary load yielding more B vitamins and less minerals, the UNSAT dietary load yielding more minerals and less B Vitamins and the CARB group yielding the least minerals and B Vitamins. We’re not as clear for the CARB group, because the authors don’t specify what candy or sweetened beverage means, but they’re probably not major contributors.
The other thing is that the UNSAT diet contributes 5-6 grams of fiber to the overall intake.
So, there’s so pretty big differences between the diets removed from fat concentration and type. To what degree this explains the differences found by the investigators between groups isn’t obvious to me, but it shouldn’t be ignored.
The limitations of this study
As the authors pointed out, it was a very small study. Additionally, they mention they didn’t assess physical activity, which is important in this context. Maybe one group was more active than the other.
Another big issue is that we don’t know what the eating patterns of the subjects were removed from what they were attempting to stuff their face with beyond their normal intake. After follow ups for compliance and assessing lipoprotein content, the authors estimated intake of fat of 60% in the SAT group and 59% in the UNSAT group. So, what comprises the other 40% and 41% of these folk’s intake? 6 days worth of dietary records are unlikely to reflect that.
The adipose gene expression markers are very interesting, but subject to interpretation, which can blur the bigger picture in the end. It would have been nice to see in addition to HOMA-IR, other clinical markers.
What does this mean for you?
- Don’t overeat.
- If you find yourself overeating or are going to be in a situation where you might do so, get make sure fibrous foods are on board.
- If a large contributor to your calories are processed foods with added oils or sugars (which you should rethink), you might work with your doctor and see how food with specific added oils and sugars impact your health and lab work.
- If you’re not overeating, I would not stress about the saturated fat content of your diet, unless you have persistent lab abnormalities. If that is the case, consider replacing the saturated fats in your diet with monounsaturated fats. That means deriving more of your calories avocados, nuts and seeds, olives instead of cheese, butter, lard, tallow and other animal fats.
- If you have pervasive chronic health issues or lab abnormalities, a trial without dairy is in order.
Recent study in humans suggesting saturated fat is more harmful than sugar and unsaturated fat in the context of overfeeding
 Luukkonen, Panu K., et al. “Saturated Fat Is More Metabolically Harmful for the Human Liver Than Unsaturated Fat or Simple Sugars.” Diabetes care (2018): dc180071
How the gut microbiome contributes to diabetes and obesity and how dietary fat may be related
 Boutagy, Nabil E., et al. “Metabolic endotoxemia with obesity: Is it real and is it relevant?.” Biochimie 124 (2016): 11-20
 Cani, Patrice D., et al. “Metabolic endotoxemia initiates obesity and insulin resistance.” Diabetes 56.7 (2007): 1761-1772
Billy Mitchell is a Naturopathic Physician specializing in rheumatology. His interests peripheral to that are clinical nutrition and environmental medicine.