Is intermittent fasting right for you?
September 24, 2025
Celebrities are often the template for summer diet trends, and this summer’s theme was intermittent fasting.
Actor Orlando Bloom revealed a dramatic 52-pound weight loss over a short period of time for an upcoming movie role. The already-trim Bloom shed pounds through extreme calorie restriction and intermittent fasting, which he says caused mood changes that made him “a horrible person to be around.”
Luka Dončić, point guard for the Los Angeles Lakers, had a much different experience with intermittent fasting. He’s showing off a leaner physique since being traded from the Dallas Mavericks in February. Dončić attributes his defined look to twice-a-day workouts and a high-protein, low-sugar, gluten-free nutrition plan – along with intermittent fasting six days a week.
On top of celebrity experiences, there is an endless supply of social media influencers touting the potential benefits of intermittent fasting, claiming swift weight loss, better focus, lower inflammation, and “detoxification” of the body.
Join us for Weight Wellness Day, a free community event on Saturday, Sept. 27, at UT Southwestern Medical Center. The event, sponsored by the UT Southwestern Nutrition and Obesity Research Center (NORC), is open to UTSW employees, patients, family members, and friends. There is no cost to attend. Lunch will be provided.
Every day, patients in our Weight Wellness Program come in with questions about whether intermittent fasting works and how to get started. The answers are different for each patient.
Concrete scientific data about the effectiveness of intermittent fasting is limited – it’s difficult to maintain any type of restricted diet long term, and it’s even tougher to account for variables outside of a lab’s control, such as changing nutritional needs with age, medical conditions, or differences in exercise habits.
While celebrities often have the advantage of working with a team of professionals to guide their nutrition and exercise 24/7, most “regular” people don’t. But what we do have is a wealth of proven strategies to optimize your nutrition and overall health alongside the eating plan you choose.
So, here are some frequently asked questions and answers to help you be safe and successful if you’re curious about intermittent fasting.
What is intermittent fasting?
In general, intermittent fasting is an eating pattern in which you cycle between periods of eating and periods of fasting (not eating) or significantly reducing your calorie intake to less than 25% of what you usually eat in a day. During this time, people usually drink only water or no-calorie beverages.
There are three main types of intermittent fasting:
- Alternate day fasting: You’ll eat normally on even days, for example, and fast on odd days.
- 5:2 approach: You’ll eat normally five days and fast two days, either on back-to-back days or separated out during the week.
- Time-restricted eating: This is what most people think of when they consider intermittent fasting. In a 24-hour period, you’ll limit food to certain timeframes such as eight hours eating and 16 hours fasting, or 10 hours eating and 14 hours fasting.
Related reading: 9 diet fads to try (or skip completely) in the new year
Does intermittent fasting work?
Clinical studies reporting outcomes on intermittent fasting are mixed, largely due to the challenging nature of nutritional research. Most studies on intermittent fasting are done on healthy, middle-aged people, and the majority of these studies are small, often with fewer than 100 participants tracked for less than a year.
Interestingly, many clinical trials involving intermittent fasting have a significant dropout rate. Even in studies where people are provided the food to eat, this pattern of eating can interfere with family dinners, social outings, and other lifestyle preferences. That speaks to the sustainability of intermittent fasting – it is difficult to do long term, which is key for any diet pattern you choose.
The bottom line: Most studies do show weight loss with intermittent fasting, however often not more than comparative low-calorie diets, so the weight loss is due to restricting calories. That's essentially how any diet is going to work. Some have also shown benefits, such as increased HDL (good) cholesterol, reduced triglycerides, or lowered blood pressure. However, some of the studies show no additional health benefits to intermittent fasting.
More research in a large, diverse population – and for a longer period of time – is needed before we can draw specific conclusions about the effectiveness of intermittent fasting at scale. And it’s crucial to note that the possible risks and benefits will vary for each person.
Are there any health risks with intermittent fasting?
Frequently, people who try intermittent fasting don’t change the quality of their diet. Eating less overall but continuing to consume less healthy food may result in short-term weight loss but will not be good for your overall health.
For some people, significantly restricting eating can be associated with metabolic health challenges. Intermittent fasting is not recommended for people who are:
- Pregnant
- Breastfeeding
- Still growing, such as teenagers
- Living with chronic conditions that have diet restrictions, such as heart failure, kidney disease, or diabetes controlled with insulin
- Living with an eating disorder
Long term, depending on your personal health, there may be concerns associated with loss of bone density or muscle mass. Women may have challenges associated with hormone changes or disruption of the menstrual cycle.
Short term, you may notice changes in your energy or strength. If it is a little tougher to pick up your child or your dog, for example, after a few months of intermittent fasting, you may not be getting proper nutrition, such as consuming enough protein.
How much protein do you need in a day?
This is a loaded question because the answer depends on several personal health and lifestyle factors as well as any weight goals. For example, a weightlifting enthusiast probably needs more protein than a weekend warrior athlete. Our Weight Wellness patients, especially if on a GLP-1 medication, are encouraged to eat protein with every meal in addition to incorporating resistance training exercises. But people with chronic kidney disease should not eat excess protein, and those with diabetes need a steady, balanced flow of nutrients to maintain blood sugar.
Recommended protein intake is often calculated based on body weight. General recommendations are 0.8 to 1 gram of protein per kilogram of body weight for healthy people 18 or older. For a 200-pound (91-kilogram) person, that would be about 72-91 grams of protein a day – and it can feel like a full-time job trying to “hit your macros.”
The key for most people in the long run is getting a good nutritional balance, including fiber, nutrient-rich whole grains, vegetables, and fruits along with sufficient protein. Talk with a registered dietitian who understands your individual health goals about the amount of protein you should eat for optimal health.
Related reading: Protein sources that strike the right balance
5 tips for safety and success
If you decide to try intermittent fasting, here are a few strategies to help you start safely and feel less uncomfortable as you adjust your eating habits.
1. Give your body time to adapt to the fasting window
As you adjust to intermittent fasting, you may experience side effects such as:
- Irritability
- Mild dehydration
- Fatigue
- Hunger pangs
- Difficulty concentrating
You may wish to start with a longer window of “eating hours,” then gradually increase the fasting hours. Note how your chosen eating pattern fits into your schedule – you may wish to realign your eating hours occasionally to participate in morning breakfast, social outings, or family dinners.
2. Eat more of your calories earlier in the day
Sometimes people aren't very hungry in the morning, and it can be tough to squeeze in a big breakfast during the morning frenzy. But eating earlier could mean more success with intermittent fasting.
An interesting randomized control study published in 2025 focused not only on time-restricted eating like most studies but also on effects of the Mediterranean diet, which focuses on whole foods, lean proteins, and healthy fats. Each participant ate the same food and had the same amount of time to eat, but some were eating early in the day.
While all participants lost weight, those who ate earlier also showed improvement in insulin sensitivity and blood sugar. This is likely because our bodies run on circadian rhythms – biological cycles that align with daytime and nighttime – and in the morning, we are more insulin sensitive. Individuals who work overnights or swing shifts may, therefore, benefit from intermittent fasting because they’re more likely to align with the body’s natural cycles. “Nighttime snackers” are another group who may benefit from intermittent fasting to help reduce intake of calorie-dense foods before bed.
3. Prioritize sleep, exercise, and hydration
Chronic sleep disruption increases the risk of weight gain, and diet- and weight-associated health problems can cause sleep problems ranging from snoring to heartburn while lying down.
If you have trouble sleeping, talk with a doctor about steps you can take to improve your sleep quality. One suggestion they’ll likely make: Get more exercise. Strength training and cardiovascular exercise offer a double benefit:
- Reducing muscle loss: Having strong muscles as we age helps to maintain mobility, flexibility, and independence.
- Improving sleep quality: Along with stress reduction, exercise encourages the release of endorphins in the brain and helps the body regulate its temperature during sleep.
Staying hydrated is essential for many of your body’s vital functions. Reduce the amount of caffeinated beverages you drink, and include water-containing fruits and vegetables in your eating hours for an extra hydration boost.
Related reading: Getting more sleep can help improve weight wellness
4. Focus on body composition, not just weight
The easiest way to monitor progress at home is with a scale, but it's not the most accurate way. Most people should not be overly focused on their weight alone.
Our Weight Wellness team encourages patients to instead consider their total body composition: muscle, fat, and bone. Throughout life, we should focus on improving bone and muscle health, which supports our overall wellness and quality of life as we age. This goes hand in hand with spotting and managing – and ideally preventing – chronic medical conditions such as high blood pressure, high cholesterol, and diabetes.
While the gold standard to analyze your body composition is through a DXA scan, which is an external device that measures your muscle-fat-bone density metrics, it can be pricey. The UTSW Weight Wellness Clinic has a scale that is helpful to analyze trends in body composition. Talk with a doctor about the appropriate ratio you should aim for in your wellness journey.
5. Partner with a provider who understands your lifestyle
Are you a cyclist, swimmer, or runner? Do you have a chronic health condition? Do you have medications that must be taken with food or drink?
All these considerations are important when determining how to safely change your eating patterns. Rather than attributing success solely to “pounds lost,” a medical provider can help you visualize the big picture of your health and wellness goals. For example, at the UT Southwestern Weight Wellness Clinic, there are obesity medicine specialists, registered dietitians, and behavioral health experts who can help you design a sustainable, effective eating and exercise plan to help you achieve your goals.
While celebrities like Bloom and Dončić made a big splash with intermittent fasting results this summer, that eating pattern may not be the best choice for you. Talk with an expert about your options. By working together, you can create a plan that moves the needle – safely, sustainably, and effectively.
To talk with an expert about intermittent fasting, make an appointment by calling 214-645-2800 or request an appointment online.
