A lot of people with diabetes delay going on insulin for as long as possible because they’ve heard horror stories about how much weight it can make them gain (or maybe they just don’t like shots or needles). Of course, people with type 1 don’t have a choice and have to use insulin to stay alive. Why is it then that using insulin usually causes weight gain, regardless of which type of diabetes you have?
It's possible that you start gaining weight when your blood glucose is more tightly controlled with insulin because you stop peeing out as many calories (glucose appears in your urine when your blood glucose exceeds your urinary threshold, which is usually around 200 mg/dl or 11.1 mmol/l). You may also be gaining from having to eat extra to treat any low blood glucose more often caused by insulin.
If you’re taking oral medications only to lower your blood glucose and they're not working, insulin may still be a viable better control, even though it can cause some weight gain. A lot of the newer medications, though, don't cause weight gain and may actually cause weight loss, such as Invokana (ironically, it works by making you pee out more glucose when your blood levels rise). Some of the newer injected medications (like Byetta) also help control your appetite and promote weight loss due to eating less.
Some studies have looked at whether weight gain is simply a result of eating more when you’re on insulin. One found that weight gain was not due to an increase in food intake, but rather that your body may increase its efficiency in using glucose and other fuels when your glycemic control improves—making you store more available energy from the foods you eat as body fat (even if you’re eating the same amount as before you went on insulin) (1).
What can you do to avoid weight gain if you have to take insulin? Try to stay in good control while using the lowest insulin doses you can because the more insulin you take, the greater your potential for weight gain is. Not surprisingly, the best way to keep your insulin needs in check is to engage in regular physical activity. In another study, some adults with type 2 diabetes gained weight from insulin use while others did not. The main difference between the “gainers” and the “non-gainers” was that the gainers were less physically active (2).
If you have type 1 diabetes, taking insulin doses that effectively manage your blood glucose can also lead to weight gain, but increasing your activity levels has been shown to prevent getting fatter (3). It's a balancing act between taking just enough insulin to keep your blood glucose in good control without having to eat extra calories to treat or prevent lows. Despite the fact that you may have been told that you can eat whatever you want to as long as you take the insulin to cover it, you will find that eating things that spike glucose quickly (like cake) or have a lot of calories digested over time (like pizza) make it much harder to match insulin to food intake and avoid excessive calorie intake and weight gain.
When you're active, your muscles can take up blood glucose and use it as a fuel without insulin. After exercise, your insulin action is heightened for a few hours and as long as 72 hours, meaning that you will need smaller doses of insulin to have the same glucose-lowering effect post-exercise. It is my personal experience that regular exercise is the best way to prevent insulin-induced weight gain, but your insulin doses will absolutely need to be adjusted downward to prevent lows that would cause you to take in extra calories to treat them.
You may also be able to avoid weight gain by taking a look at the type of insulins that you are using. For example, in overweight type 2 diabetic subjects, use of once-daily Levemir caused less weight gain and less frequent hypoglycemia than use of NPH (4), even combined with use of rapid-acting injections of a separate insulin for meals--and the same is likely true when using Lantus. Anyone taking basal insulin alone (once or twice daily) or following a basal-bolus regimen can benefit by making sure that insulin doses are regulated effectively to prevent blood glucose lows and highs while using as little insulin as absolutely necessary. In other words, the type of insulin you use and the doses you take are both important to consider in the overall management of your diabetes and your body weight, regardless of which type of diabetes you have.
Just as importantly, though, is how you choose to manage your lifestyle, both your exercise and your dietary choices. Changes in your lifestyle, such as cutting back on refined carbohydrates that require larger doses of insulin to cover them and exercising regularly, are likely your best bets to counteract any potential weight gain caused by insulin use. An added side benefit is that if you have type 2 diabetes and start exercising regularly, you may actually lose fat weight and be able to lower your insulin doses more or get off of insulin injections completely.
References:
Jacob AN et al. Weight gain in type 2 diabetes mellitus. Diabetes Obes Metab. 2007 May;9(3):386-93.
Jansen HJ et al. Pronounced weight gain in insulin-treated patients with type 2 diabetes mellitus is associated with an unfavourable cardiometabolic risk profile. Neth J Med. 2010 Nov;68(11):359-66.
Jacob AN et al. Potential causes of weight gain in type 1 diabetes mellitus. Diabetes Obes Metab. 2006 Jul;8(4):404-11.
Fajardo Montañana C et al. Less weight gain and hypoglycaemia with once-daily insulin detemir than NPH insulin in intensification of insulin therapy in overweight Type 2 diabetes patients: the PREDICTIVE BMI clinical trial. Diabet Med. 2008 Aug;25(8):916-23.