Ask Keri: It seems like everyone is talking about intermittent fasting. As an RD, do you recommend the practice?
Keri says: It really does feel like absolutely everyone is preaching the benefits of intermittent fasting. Weight loss! Brain health! A longer life!
My perspective, in a nutshell: the early research got a lot of people excited, me included. But the more rigorous studies that followed have been far less impressive, and for women, especially women in midlife, I think the downsides often outweigh the benefits. It’s also a regimented way of eating that many people find too hard to fit around work hours, family, and a social life.
Here are the details you need to figure out if it’s right for you.
What is intermittent fasting?
Intermittent fasting is a broad term that covers a pattern of eating that involves a set amount of time where you don’t eat (or eat an incredibly restricted number of calories), followed by one in which you do.
The most popular version involves fitting all of your daily food consumption into an eight-hour window, followed by 16 hours of fasting. For example, you could eat between 10 a.m. and 6 p.m. every day and fast between 6 p.m. and 10 a.m. (including the hours you’re asleep). There’s also the 5:2 diet in which you split your week into five days of eating whenever you want and two days where you seriously restrict your calories—500 for women, 600 for men. (Personally, I find this one to be the easiest of the options.)
While fasting may seem extreme and irregular, proponents argue that humans actually ate this way for most of history, since hunters-gatherers ate when food was available, not at set mealtimes. Plus, fasting is an age-old part of nearly every religious tradition.
The potential benefits of intermittent fasting
The early research on intermittent fasting is pretty interesting, and it’s why the trend took off. Just keep in mind that much of it comes from small, short-term studies or from animals, so read “may” and “suggests” as exactly that.
Most people try it for weight loss. Research in patients with Type 2 diabetes suggests it can help. The most basic reason it can work for weight loss is that you’re simply going to eat less when restricting calories to set time periods. When your body isn’t getting energy from food, it also turns to its other fuel source: stored fat.
Here’s what’s changed since the early hype, though. When researchers put intermittent fasting head-to-head with simply eating a bit less, it doesn’t come out ahead. In a year-long trial published in the New England Journal of Medicine, people who ate within an eight-hour window lost no more weight than people who cut the same calories without watching the clock. And a 2024 review of 29 trials found the effect of time-restricted eating on weight was small and of uncertain clinical importance.
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In terms of the bigger health picture, some studies link intermittent fasting to reducing markers of inflammation. Small, short-term studies also suggest fasting can affect hormones, increasing production of ones like HGH (which plays a role in muscle and fat metabolism) and BDNF (for cognition) while decreasing insulin levels. Whether those short-term shifts add up to real-world results is still an open question.
Fasting may lead to improvements in pancreatic B-cell function and the regulation of the circadian rhythm, which promotes better glucose tolerance. In a randomized controlled study of more than 100 overweight or obese women, six months of intermittent fasting reduced insulin levels by 29% and insulin resistance by 19%. Reductions in fasting insulin and insulin resistance were modest in both the intermittent fasting and continuous energy restriction groups, but greater in the intermittent fasting subjects. Another study on non-obese subjects also found that fasting decreased insulin levels and increased fat oxidation—the process that breaks down fat during energy restriction or exercise.
Some studies have found that fasting may improve depression and stress levels, and encourage overall positive psychological shifts. The research here is early, and it doesn’t match everyone’s experience.
Research (some in animals, some in humans) even suggests intermittent fasting’s cardiovascular and brain health benefits could extend lifespan. That’s a long way from proven in people.
There are certain groups of women who it may work well for. It's important to monitor how you feel, how you are sleeping, what your mood is like and what your menstrual cycle is like as well. Also, it may be helpful for women with PMOS (polyendocrine metabolic ovary syndrome, the new name for PCOS). Like most things with diet, it is very individual and if you choose to give it a go, you should probably work with an RD or nutrition coach.
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Are there risks to intermittent fasting?
So far, this all sounds really good, right? Here’s where I pump the brakes, especially if you’re a woman in your 40s, 50s, or beyond.
Low calorie intake always comes with risks, which is why it is important to ensure that you are getting adequate calories and proper nutrients while following this style of eating. Hunger can be a real issue, which, in turn, can lead to stress. Prolonged stress of any sort can increase inflammation in the body.
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Confining yourself to a specific way of eating for a short time can also lead you down a long road of yo-yo dieting, and a large Canadian study of teens and young adults linked intermittent fasting to disordered eating behaviors, most consistently in women. If you have any history of disordered eating, skip it.
Finally, the results of some animal studies suggest intermittent fasting could affect fertility in women, so you should skip it if you’re trying to get pregnant.
Why I’m more cautious for women in midlife
This is the part most people skip. Much of the buzzy fasting research was done in animals, in men, or in mixed groups, and women in perimenopause are often left out of studies altogether. So when someone tells you fasting is proven to work for midlife women, the honest answer is that we don’t have that data.
What we do have gives me pause. Muscle is one of your most valuable assets in midlife, and it gets harder to hold on to after 40. In a 12-week trial in JAMA Internal Medicine, people following a 16:8 schedule didn’t lose meaningfully more weight than people eating three meals a day, and among those who had body scans, the fasting group lost more lean mass in their arms and legs. A shorter eating window also makes it harder to spread enough protein across the day, which is exactly what your muscles need right now.
Then there’s the stress piece. Going long stretches without food is a stressor on the body. For some people that’s no big deal. But if you’re already running on short sleep, hot flashes, and a full plate at work and at home, piling on one more stressor can backfire. The research on fasting and cortisol, your main stress hormone, is mixed. And one small study found that eight weeks of a very narrow eating window lowered DHEA, a building block for estrogen, in both pre- and postmenopausal women (other sex hormones didn’t change). We don’t know yet what that means long-term, but it’s a reason for caution, not a green light.
The trap I’d watch for: skipping breakfast, coming up short on protein, getting overly hungry by late afternoon, and overeating at night. That’s the opposite of what supports energy, sleep, and weight health in midlife.
The bottom line
At the end of the day, my feelings on intermittent fasting boil down to a few questions: Is it going to be doable for you? Will it make healthy eating easier or harder for you?
And if you’re a woman in midlife, I’d add one more: Is this helping you protect your muscle, your sleep, and your stress levels, or working against them? For most midlife women, I think a steady eating rhythm does more good than a strict fasting window. Think a protein-rich breakfast, balanced meals through the day, and a natural overnight break of about 12 hours between dinner and breakfast.
Some people say it simplifies their eating, but if you work long, unpredictable hours and have trouble planning meals ahead, trying to stick to a plan like this may drive you crazy. It also won’t work if you’re someone whose social life often revolves around food. Spontaneous dinner dates with friends or late-night tapas after a concert? Buh-bye.
If you do think it might work for you, make sure you’re still eating in a healthy way, which means getting all of the proper nutrients from the calories you are consuming. Focusing on real, whole foods and skipping the junk will prevent nutrient deficiencies.
If it sounds like the wrong approach, don’t beat yourself up about missing out on potential benefits. Just continue with a balanced, healthy diet and be mindful of your hunger quotient to keep overeating at bay and maintain a healthy lifestyle.