For decades, different dietary interventions have emerged claiming to help individuals lose weight. Some have been proposed to also improve patients’ diabetes control. Over the past few years, intermittent fasting has become a popular weight loss trend.
While there are a variety of plans, essentially intermittent fasting involves restriction of energy intake for several days per week. Many of my patients ask whether intermittent fasting is beneficial for their diabetes management or may have troublesome effects.
Although it is easy to be swayed by the social media, my approach is to always resort to the available scientific literature. For me, dietary interventions are no different than prescribing a medication. Both diet and medication can have beneficial or unwanted effects.
What do we really know about intermittent fasting with respect to weight loss?
Of course, reducing food intake is intuitively associated with weight loss since energy expenditure may overcome energy intake. On the other hand, intermittent fasting has been practiced for centuries for religious reasons and its effect on weight is not straightforward.
For example, as many as two thirds of families who fast each day during Ramadan report weight gain rather than weight loss. This is because once eating is allowed at the end of the day, overeating can occur.
Several clinical trials have compared intermittent fasting to other dietary interventions and have not shown clinically meaningful differences in terms of weight changes and other clinical outcomes. Accordingly, my opinion is that intermittent fasting is no different than other diets.
The best diet for a person is the one that helps them to lose weight and more importantly keep it down.
What do we really know about intermittent fasting with respect to type 2 diabetes management?
The single most important objective in diabetes management is to maintain healthy glucose levels over time, or HbA1c, using any available therapeutic option. This is the most established way to prevent complications and premature death.
Remember, type 2 diabetes is a progressive condition of insulin deficiency. This means that over time, patients inevitably lose their own insulin secretion and therefore different medications need to be introduced in different stages.
In the early stages of the disease, patients still secrete a limited amount of residual insulin from their own pancreas and can maintain healthy glucose levels by using oral medications. At that very early stage, dietary interventions associated with weight loss can sometimes help to improve glucose levels and slow down the progression of insulin deficiency. Yet, over time this residual insulin secretion is lost, and patients need to add medications.
After a decade with type 2 diabetes, most patients inevitably require insulin therapy since this is the only medication that can reduce glucose. At that stage, dietary interventions typically do not help. Regarding intermittent fasting, the data is very limited and does not show clinically significant advantage over other diet interventions.
Are there side effects from intermittent fasting?
The main side effect I have seen from intermittent fasting is the same as from other extreme dietary interventions. Namely, poor glucose control. The single major priority of diabetes management is maintaining healthy glucose levels over time, or appropriate HbA1c. When a person embarks on intense diet regimens, it can dramatically change their treatment requirements.
Often, anti-diabetes medications should be modified to accommodate this lifestyle change. Yet, more often than not, people stop following the diet over time and treatment requirements rise without the patient or the doctor knowing it. Even half a year with poor glycemic control due to inconsistency in dietary use is an enormous loss. The accumulated damage during that time is just too great.
I just cannot overstate it, the most important goal is to maintain good HbA1c at all times. In my opinion, a person should choose to follow any diet that they prefer as long as they do not neglect this treatment priority.