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There’s been a ton of research around intermittent fasting over the past few years, but the latest evidence suggests that it can lead to similar weight loss results as a calorie-restricted diet. But intermittent fasting may have an edge in some areas, including helping you lose certain types of fat.
That’s the major finding of a new study published in the journal Nature Medicine. But what kind of fat are we talking about here and how can you approach intermittent fasting safely if you’re interested in going this route? Here’s what the study found, plus what a dietitian wants you to know.
Meet the expert: Scott Keatley, RD, is co-owner of Keatley Medical Nutrition Therapy
What were the findings of the study?
In a study conducted in Spain, researchers implemented a 12-week dietary intervention involving 197 individuals suffering from obesity.
The participants in the study were instructed to adhere to one of three distinct fasting approaches:
- Fasting between 5 pm to 9 am.
- Fasting from 2 pm to 10 pm.
- Fasting during a time slot they preferred (most chose between 8 am and 12 pm).
A different group recently participated in a nutritional education program that all study participants also completed.
The researchers discovered that intermittent fasting did not appear to offer any extra advantages compared to the nutritional education group in terms of decreasing visceral fat, which is the fat that encases various organs in the body.
However, the fasting groups experienced greater weight loss, averaging between 6.6 to 8.8 pounds, in contrast to the control group. Those who fasted from 5 pm to 9 am showed a more significant reduction in subcutaneous fat, particularly in the abdominal region.
Intermittent fasting may result in greater weight loss compared to a calorie-controlled group for several reasons. Firstly, intermittent fasting can help regulate insulin levels, promoting fat burning and reducing fat storage. Additionally, the eating windows in intermittent fasting might lead to a natural reduction in calorie intake, as individuals have fewer opportunities to eat throughout the day. This approach can also enhance metabolic flexibility, allowing the body to switch between burning carbohydrates and fats more efficiently. Furthermore, intermittent fasting may improve adherence to dietary changes as it simplifies meal planning and reduces the frequency of meals, leading to better long-term compliance and weight loss outcomes.
The situation is ambiguous. It’s possible that the participants in the study had limited time for meals, disrupting their usual eating habits.
In Spain, the typical breakfast time falls between 7 a.m. and 8 a.m., while dinner is usually served from 9 p.m. to 10 p.m. This results in a daily eating window of 12 to 14 hours. The practice of intermittent fasting has shortened this eating window, potentially leading to a reduction in overall food intake.
Intermittent fasting may have been more effective in reducing belly fat compared to the calorie-controlled group due to several factors. Firstly, intermittent fasting can enhance metabolic flexibility, leading to improved fat oxidation and a greater reliance on stored fat for energy during fasting periods. Secondly, it may help regulate hormones such as insulin and growth hormone, which play crucial roles in fat metabolism and fat loss. Additionally, the structured eating windows of intermittent fasting can lead to a natural reduction in calorie intake, while also promoting adherence due to the simplicity of the approach. Lastly, intermittent fasting may also influence gut health and inflammation, which are linked to fat accumulation, particularly around the abdomen.
The researchers did not specify the reasons behind the potential reduction in belly fat associated with this strategy. Nonetheless, they highlighted that adhering to an intermittent fasting regimen encourages individuals to maintain a regular pattern of eating and fasting, which can aid in stabilizing their biological rhythms.
Conversely, consuming meals at inconsistent times may disrupt these natural rhythms, raising the likelihood of obesity, cardiovascular issues, and type 2 diabetes.
Fasting can lead to improved glucose control for several reasons: 1. **Insulin Sensitivity**: Fasting can enhance insulin sensitivity, allowing the body to use insulin more effectively. This means that cells are better able to take up glucose from the bloodstream, leading to lower blood sugar levels. 2. **Reduced Caloric Intake**: By limiting food intake, fasting naturally reduces overall caloric consumption, which can help with weight loss and, in turn, improve glucose metabolism. 3. **Hormonal Changes**: Fasting triggers hormonal changes that can aid in glucose regulation. For example, levels of growth hormone and norepinephrine can increase, which helps mobilize stored fat for energy and can improve glucose utilization. 4. **Decreased Inflammation**: Fasting can reduce inflammation in the body, which is often linked to insulin resistance and poor glucose control. 5. **Autophagy**: The fasting state can promote autophagy, a process where the body cleans out damaged cells and regenerates new ones, potentially improving metabolic functions. Overall, these factors contribute to better glucose control during and after fasting periods.
The researchers did not establish this conclusion, but they speculated that it could be related to the regularity of eating patterns.
“It’s worth noting that just about any form of calorie restriction tends to lower blood glucose levels, making it difficult to separate the benefits of intermittent fasting from overall caloric reduction,” says Scott Keatley, RD, co-owner of Keatley Medical Nutrition Therapy.
Do the findings apply to individuals who are not obese?
It's difficult to determine definitively. Research has shown varied outcomes regarding the effectiveness of intermittent fasting for weight loss, often suggesting that it may be comparable to a calorie-restricted diet. However, the majority of studies examining the effects of intermittent fasting on weight loss have focused primarily on individuals with obesity.
However, this doesn't imply that it can't be a successful weight loss strategy for others; the outcomes may simply not be as pronounced.
Do the results apply to individuals in the United States?
It's difficult to determine for certain. The dietary practices in Spain significantly differ from those commonly found in the United States. Nevertheless, research on intermittent fasting has indicated that it can assist individuals in shedding pounds in various studies.
To start intermittent fasting safely, follow these steps: 1. **Consult a Healthcare Professional**: Before beginning any fasting regimen, it's important to talk to your doctor, especially if you have underlying health conditions or concerns. 2. **Choose a Fasting Method**: There are several approaches to intermittent fasting, such as the 16/8 method (fasting for 16 hours and eating during an 8-hour window), the 5:2 method (eating normally for 5 days and restricting calories on 2 days), or alternate-day fasting. Pick one that fits your lifestyle. 3. **Start Gradually**: If you're new to fasting, ease into it. Begin with shorter fasting periods and gradually increase the duration as your body adjusts. 4. **Stay Hydrated**: Drink plenty of water during fasting periods to stay hydrated. Herbal teas or black coffee (without sugar) can also be consumed. 5. **Focus on Nutrient-Dense Foods**: When you eat, prioritize whole, nutrient-dense foods like fruits, vegetables, lean proteins, and healthy fats to ensure you're getting the necessary vitamins and minerals. 6. **Listen to Your Body**: Pay attention to how your body responds. If you feel dizzy, overly fatigued, or unwell, reconsider your approach and consult a healthcare professional. 7. **Maintain a Balanced Lifestyle**: Incorporate regular physical activity, manage stress, and ensure you’re getting enough sleep to support your overall health during fasting. By following these guidelines, you can start intermittent fasting in a safe and effective manner.
According to Keatley, adopting a "careful and gradual method" is the most effective way to approach intermittent fasting.
If you suffer from any pre-existing health conditions such as diabetes or digestive problems, it is advisable to seek guidance from a healthcare professional to ensure that this approach is suitable for you. Following that, he suggests, “start by slowly adjusting your meal times to finish earlier in the evening, which will help your body adapt more easily.”
Keatley recommends prioritizing nutrient-rich meals that include a balance of macronutrients—such as protein, healthy fats, and fiber—during the eating window. This approach can help maintain your energy levels and curb hunger during fasting periods.
“Staying hydrated is essential, so make sure to consume ample amounts of water, herbal tea, or black coffee while you’re fasting,” advises Keatley. “Keep an eye on how your body reacts to fasting, being mindful of symptoms such as tiredness, lightheadedness, or mood swings, and make adjustments if necessary.”
Maintaining other healthy habits is crucial as well, such as engaging in regular physical activity, with a particular emphasis on strength training to maintain muscle mass during fat loss. "Ultimately, it's essential to focus on consistency and patience, as it may take time to see changes in blood sugar levels and fat reduction," Keatley advises.
Korin Miller is a freelance writer with expertise in general wellness, sexual health and relationships, and lifestyle trends. Her work has been featured in publications such as Men’s Health, Women’s Health, Self, and Glamour. She holds a master’s degree from American University, resides near the beach, and dreams of owning a teacup pig and a taco truck in the future.
