The perpetual search for the secret for a long and healthy life often takes a detour when new dietary recommendations emerge. For decades, the dogma has been that long-chain saturated fat in the diet could lead to such diseases as type 2 diabetes. However, new research involving humans and mice shows that saturated fat does not harm health.
Obesity, heart problems and type 2 diabetes are a huge and growing problem in modern society. The quest to understand how to avoid disease by changing lifestyle is therefore massive, and both diet and exercise play significant roles. Although the mechanisms are very complex, new studies of humans and mice on how a high-fat diet affects insulin sensitivity and diabetes solve some of the mystery.
“For decades, saturated fat has been trumpeted as causing type 2 diabetes and other diseases. However, our latest experiments suggest that the fear of fat is exaggerated and that ensuring energy balance in the diet is more important,” explains the initiator of the new study, Bente Kiens, Professor, Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen.
Overeating is the problem
Many efforts have been made to reduce saturated fat in the modern diet, since several population-based studies suggested that eating saturated fat increases the risk of lifestyle-related diseases. This dogma was recently challenged in 2019 when Bente Kiens and her research team showed that saturated fat did not negatively affect many important health indicators among healthy but slightly overweight participants.
“As long as the participants did not consume more calories than they used, both blood and tissue samples revealed that the participants’ were equally healthy whether they ate mainly carbohydrate or mainly saturated or unsaturated fat. The body simply adjusts to burning fat instead of glucose. In our new experiment, we wanted to test whether the type of fat made a difference, and we were surprised to find no difference between saturated and unsaturated fat in how they affected several health parameters,” explains Annemarie Lundsgaard, Postdoctoral Fellow, Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen.
The researchers exposed two groups of slightly overweight men to two types of high-fat diets for 6 weeks, with fat comprising 64% of total energy intake, which was 30 energy % more than their habitual diet. All participants were in energy balance, but the high-fat diet in one group comprised predominantly saturated fat and the other primarily unsaturated fat. The carbohydrate intake was reduced to 20% of total energy intake, which was about 25 energy % lower than in the habitual diet.
“Their triglyceride levels in the blood declined substantially regardless of whether their high-fat diet was predominantly saturated or unsaturated, which would surprise most people. Liver health improved, and there were no adverse effects on insulin action. In contrast, if you eat more calories than you use, then such a diet will negatively affect insulin sensitivity, regardless of whether the diet predominantly comprises fat or carbohydrate,” says Annemarie Lundsgaard.
A tiny change made the difference
In another trial, the participating men ate a high-fat diet for just 3 days, but this time they were in substantial energy surplus and developed clear insulin resistance and thus the early stages of what can lead to diabetes with a permanently elevated intake. This happened regardless of whether the participants consumed long-chain saturated or unsaturated fat, which is the most common type in animal and vegetable fats. However, in this overfeeding study, the research group made another surprising finding related to the chain length of the fatty acids. “We gave another group of men a similar high-fat diet, except we replaced 30 grams of the long-chain saturated fat with 30 grams of medium-chain saturated fat, which can befound in, for example, coconut oil and palm kernel oil and certain dairy products. Interestingly, this completely eliminated insulin resistance. This means that replacing just 30 g of the 450 g total fat that the subjects consumed with 30 g of medium-chain fat prevented the participants from developing insulin resistance. This is really exciting!” says Bente Kiens.
The researchers do not yet know the exact reason for the remarkable results, but Bente Kiens thinks that at least the fear of fat and even saturated fat should be eliminated, as long as you do not consume too many calories overall.
“So eating fat is okay, whereas eating too many calories is not. However, in addition to highlighting the need for more nuanced dietary guidelines for saturated fat, the new results show a great potential for using medium-chain saturated fat as a supplement for regulating both fat and glucose metabolism. The mechanisms for the remarkable effect of medium-chain fatty acids remain to be revealed,” concludes Bente Kiens.