No matter what intermittent fasting schedule [1] you're on, if you found that you're not losing weight or you've hit a weight-loss plateau, it could be because you're not clean fasting.

What is Clean Fasting?

According to cardiologist and weight management expert Luize Petre [2], MD, intermittent fasting [3] involves alternating periods of eating, or "feasting," with periods of not eating, or "fasting." The fasting window can be done in various ways, either with allowance of very low-caloric foods or liquids or by restricting it to only zero-calorie liquids. "When the more restrictive approach is taken, that is called clean fasting," she explained.

Clean fasting often is used to describe fasting or time-restricted feeding where only calorie-free and unsweetened beverages are consumed; in other words, Erin Donaldson, DO, with Executive Medicine of Texas [4], said stick to water, sparkling water, black coffee, tea, and herbal teas with nothing else added — not even lemon slices or a noncaloric natural sweetener like stevia or monk fruit.

Can I Have Artificial Sweeteners or Cream While Fasting?

Many experts will say a little cream, MCT oil, sugar-free sweetener, or stevia is OK to have in your coffee while fasting, also known as "dirty fasting." But for maximum results, especially if you're not achieving your weight-loss goals, "the fast should be kept clean, and all artificial sweeteners should be avoided," said Dr. Donaldson.

Dr. Petre adds that sugar-free sweeteners can raise your insulin levels initially, and that's because your taste buds tell the brain that sugar is coming and the body prepares in advance for insulin secretion [5]. Studies suggest that stevia can also raise insulin levels [6], so that should be avoided as well.

When insulin levels are low, it cues our bodies to use stored fat for energy, explained Dr. Donaldson. And even though you think you're still fasting because you're only drinking coffee with a little sugar-free sweetener or cream, or you're consuming something under 35 calories, if your body produces insulin, then it won't turn to your stored fat for energy.

Can I Have Sugar-Free Beverages While Fasting?

Your body will have the same response to sugar-free beverages such as sodas and sports drinks, said Dr. Petre, so it's best to avoid these as well and stick to clean fasting.

Can I Have Sugarless Gum While Fasting?

If gum is sweetened with artificial sweeteners, then yes, it could also trigger insulin secretion as discussed above due to the taste buds and brain connection, explained Dr. Petre.

Another issue with chewing gum [7] or consuming a sugar-free beverage while fasting, explained Dr. Jason Fung, MD, a nephrologist (kidney specialist) and author of The Complete Guide to Fasting [8], is that "gum is usually not recommended because the act of chewing and the sweetness usually triggers salivation and hunger." So for some, even if you chew sugarless gum or drink a diet soda, it might actually make fasting harder.

Do I Have to Clean Fast?

Don Brown, MD, CEO and founder of the LIFE Fasting app, said "the popular concept of clean fasting doesn't necessarily have a strong scientific rationale." The important thing is that in clinical research studies, even when people consume a small number of calories, flavoured water, broth [9], or other artificially sweetened, calorie-free beverages while fasting, intermittent fasting for periods of 16 or more hours has been shown to have measurable health benefits.

If you're feeling great intermittent fasting and sipping on coffee with a little cream and stevia, chewing gum, or drinking sugar-free beverages, then I say that's a win! But if you're not feeling great or achieving the weight-loss results you want, it's worth trying clean fasting.