Dietary Fat and Blood Sugar: Should I Bolus for Fat?


Say it isn’t so… A study of dietary fat and blood sugar suggests I might need to bolus for fat!  According to a Joslin study whose findings appeared in the April issue of Diabetes Care, dietary fat can affect blood sugar levels and insulin requirements for people with type 1 diabetes.  There goes my theory that I can eat mozzarella by the pound without a budge in blood sugar.  And what about my almond butter?  Are all those spoonfuls of nut butter screwing with my blood sugar?  Not according to my glucometer, but yes according to Joslin researchers:

Fat and Blood Sugar- Do I need to bolus for this?In reviews of continuous glucose monitoring and food log data from adult patients with type 1 diabetes, Joslin clinicians observed that  “several hours after eating high-fat meals, glucose levels went up,” says study lead author Howard Wolpert, MD, Senior Physician in the Joslin Clinic Section on Adult Diabetes and the Director of the Insulin Pump Program at Joslin. “We wanted to determine the underlying cause of these unexplained fluctuations.”

In Dr. Wolpert’s study, seven participants (adults with type 1 diabetes with an average age of 55) spent two days at Beth Israel Deaconess Medical Center eating carefully controlled meals and having their glucose and insulin levels monitored.

“All breakfasts and lunches featured identical low-fat content. The two dinners had identical carbohydrate and protein content but one was low-fat and the other high-fat. For two 18-hour periods beginning before dinner, participants had their insulin automatically regulated by a closed-loop system and their glucose and plasma insulin levels tested at frequent intervals.

Study results showed that participants required more insulin after eating the high-fat dinner than the low-fat dinner (12.6 units compared to 9 units). In contrast, the two breakfast meals required similar insulin doses. Despite the increased insulin, participants had greater hyperglycemia after the high-fat dinner with insulin levels elevated five to ten hours after the meal.  The average increase in insulin was 42 percent with significant individual differences.”

So what does this mean?  According to Dr. Wolpert, “These findings highlight the limitations of basing mealtime insulin dosing for type 1 diabetes solely on carbohydrate intake.”  

Mike always boluses for protein as well as carbohydrate, but neither of us thinks much about fat.  In fact, to my mind it’s pretty much a free food.  This study makes me very curious about the ketogenic diet and type 1 diabetes.  I’ve never eaten low carb enough to consider myself on a ketogenic diet, but I don’t skimp on fat, and as long as I don’t eat carbs, my blood glucose is usually in the normal range.

Apparently another study is planned “to assess whether reducing fat intake would optimize glucose control.” And, “in the coming months, Dr. Wolpert also anticipates developing new guidelines for clinicians and patients to enable them to determine whether high-fat foods are a factor in glucose control and make appropriate nutritional changes.”

Meanwhile… I guess I’ll eat more cucumbers


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vladPeggy HollowayJessica AppleJohn FitzgeraldBernard Farrell Recent comment authors
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Fat does not require insulin for metabolism, but fat creates a temporary insulin resistance effect.

Peggy Holloway
Peggy Holloway

It scientifically makes no sense. Fat does not require insulin for metabolism. To make this experiment valid, only fat should be consumed. The fact that protein and carbohydrate are still present are undoubtedly influencing the results.

John Fitzgerald
John Fitzgerald

Dr. Wolpert’s experiment is no surprise. I have been following the same path described by Ann as part of my weight loss efforts. Both protein and fat are metabolised at a slower rate than carbs so I actually delay my bolus a little to match the peaks from the gluconeogenesis of the fats and proteins. My A1c dropped to 6.6 after I started this regimen and I suspect it will be lower after a full 3 months. It is funny but I also use a spreadsheet. Multiply the grams of protein by .6 and the grams of carb by .1… Read more »

Bernard Farrell
Bernard Farrell

If I have 3 slices of pizza at dinner, my blood sugar will be screwed up all night long. I’ve found one way to reduce the impact is to take a bolus spread over 6 hours that adds 0.4 to 0.6 units each hour. I don’t take this as a basal increase because I want to track the IOB. My CDE has talked to me about an insulin to fat ratio. She suggests that for high-fat meals I’d take a bolus that’s set for 8 hours. I guess I should try that next. Developing an insulin/fat ratio would be difficult… Read more »


I bolus for both protein and fat. For me, the best thing is to calculate 58% of protein intake in grams and divide that by my insulin:carb ratio. I also calculate 10% of my fat intake in grams, and divide that by my insulin:carb ratio. I add those two numbers together with the insulin:carb ratio for the carbohydrates in the meal. The result is the amount of insulin I need. I have a little spreadsheet that does the work for me. I’ve been doing this for 18 months with excellent results, including a steady A1c of 5.4 mmol/L. I rarely… Read more »


Thanks very much for the article! The impact of fat on blood sugar has already been embraced by at least some doctors and patients f.ex. in Germany. Some PWDs there include fat and protein in their bolus calculations using so called “fat-protein-units” and including those in an extended bolus. I have not started to do this yet, but I have definitely noticed the impact of both protein and fat on my bgs (especially after eating nuts or nut butters!).
I would be interested to hear from people who already include fat (and protein) in their bolus calculations. 

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