Scientists looked at 15 different studies involving 862 people to understand how weight loss affects a special brain chemical called BDNF. This chemical helps your brain work better and may control hunger and energy levels. The research found that different types of diets affected BDNF differently—some diets increased it, some had no effect, and a few actually decreased it. Intermittent fasting and Mediterranean-style diets seemed most likely to boost BDNF levels, while regular calorie counting showed mixed results. The findings suggest that how you lose weight might matter just as much as how much weight you lose when it comes to brain health.

The Quick Take

  • What they studied: Whether different types of weight-loss diets change the levels of a brain chemical called BDNF that affects thinking, mood, and hunger control
  • Who participated: 862 adults across 15 different studies who were overweight or obese and tried various weight-loss diets for 6 to 26 weeks
  • Key finding: Different diets had different effects on BDNF: intermittent fasting and Mediterranean diets tended to increase it, regular calorie restriction showed mixed results, and very rapid weight loss sometimes decreased it
  • What it means for you: If you’re trying to lose weight, the type of diet you choose might affect your brain health and mood, not just your waistline. However, more research is needed to confirm these findings and understand which approach works best for different people.

The Research Details

This was a systematic review, which means researchers searched through all available scientific studies on this topic and summarized what they found. They looked at studies published up until April 2025 in major scientific databases. The researchers included 15 clinical trials—11 were randomized controlled trials (where people were randomly assigned to different diets) and 4 were single-arm trials (where everyone followed the same diet). The studies tested different weight-loss approaches: regular calorie restriction (eating 20-30% fewer calories), intermittent fasting (eating normally some days and restricting calories on others), ketogenic diets (very low-carb diets), Mediterranean diets, and other weight-loss programs. All studies measured BDNF levels before and after the diet, and all lasted at least 4 weeks.

The researchers followed strict guidelines called PRISMA standards to make sure they conducted the review properly and fairly. They checked each study for potential problems or bias that might affect the results. They then organized all the information they found into categories based on whether BDNF went up, stayed the same, or went down with each type of diet.

Understanding how different diets affect BDNF is important because this brain chemical does more than just help you think—it also influences mood, memory, and how your body controls hunger and energy. By looking at multiple studies together, researchers can see patterns that might not be obvious in just one study. This helps us understand whether weight loss itself is what matters for brain health, or whether the specific way you lose weight makes a difference.

This review included both randomized controlled trials (the gold standard in research) and smaller single-arm trials, which is good for getting a complete picture. However, the studies varied quite a bit in how long they lasted (6 to 26 weeks), what diets they tested, and how they measured BDNF. This variation makes it harder to draw firm conclusions. The researchers assessed each study for bias using established tools, which helps readers understand how reliable each study was. The fact that results were mixed across studies suggests that more high-quality research is needed to fully understand this topic.

What the Results Show

The research found that weight-loss diets affect BDNF in different ways depending on the type of diet. About half of all the studies showed no significant change in BDNF levels after weight loss, which was surprising to many researchers. A few studies actually found that BDNF decreased, particularly when people lost weight very quickly through extreme calorie restriction.

However, certain diets showed more promise for increasing BDNF. Intermittent fasting approaches—where people eat normally on some days and restrict calories on others—tended to increase BDNF levels more often than other methods. The Mediterranean-DASH-MIND diet (a combination of three healthy eating patterns) also frequently increased BDNF. Ketogenic diets (very low-carbohydrate diets) also showed promise for raising BDNF in several studies.

In contrast, continuous calorie restriction—the traditional approach of eating fewer calories every single day—produced mixed results. Some people’s BDNF went up, some stayed the same, and some went down. This suggests that the way you restrict calories might matter more than simply eating less overall.

Interestingly, the research suggests that losing weight very rapidly might actually be counterproductive for BDNF levels. This could mean that slower, more gradual weight loss might be better for your brain health, even if it takes longer to see results on the scale.

The studies also looked at how BDNF changes related to other health improvements. The research confirmed that people with obesity tend to have lower BDNF levels to begin with, and that BDNF is connected to better thinking skills, better mood, and better control of hunger and energy. The findings suggest that by choosing the right type of diet, you might be able to improve not just your weight, but also these other important health markers. However, the studies didn’t always measure these other outcomes, so more research is needed to confirm these connections.

Previous research had shown that BDNF is important for brain health and that obesity is linked to lower BDNF levels. This systematic review adds to that knowledge by showing that weight loss itself doesn’t automatically fix BDNF levels—the way you lose weight appears to matter. This finding is relatively new and suggests that future weight-loss advice might need to consider not just how much weight people lose, but also which diet methods are best for brain health. The mixed results across studies also highlight that we still have much to learn about this topic.

This review has several important limitations. First, the 15 studies included were quite different from each other in terms of diet type, study length, and how they measured BDNF, making it hard to draw firm conclusions. Second, most studies were relatively short (6 to 26 weeks), so we don’t know if BDNF changes last over months or years. Third, the studies included relatively small numbers of people, and we don’t know if results would be the same for different age groups, ethnicities, or people with different health conditions. Fourth, some studies were better quality than others, which affects how much we can trust the overall findings. Finally, the research doesn’t tell us whether increases in BDNF actually lead to real improvements in brain function or mood in everyday life—that would require additional studies.

The Bottom Line

Based on this research, if you’re trying to lose weight and want to support your brain health, intermittent fasting, Mediterranean-style diets, or ketogenic diets may be worth considering, as these showed more consistent increases in BDNF. However, the evidence is still developing, so these recommendations should be considered preliminary rather than definitive. If you choose continuous calorie restriction (traditional dieting), be aware that it may not increase BDNF, though it can still help you lose weight. Avoid very rapid weight loss if possible, as this may actually decrease BDNF. Most importantly, choose a diet approach you can stick with long-term, as consistency matters more than perfection. Consult with a healthcare provider or registered dietitian before starting any new diet, especially if you have health conditions or take medications.

This research is most relevant for adults who are overweight or obese and considering weight-loss diets. It’s particularly interesting for people who care about brain health, mood, and cognitive function, not just weight loss. People with depression, anxiety, or cognitive concerns might find this especially relevant. However, these findings shouldn’t replace medical advice from your doctor. People with certain medical conditions, eating disorders, or those taking specific medications should talk to their healthcare provider before making major diet changes. The research is less clear about whether these findings apply to people of normal weight or to children and teenagers.

Based on the studies reviewed, changes in BDNF levels appeared within 6 to 26 weeks of starting a diet. However, this doesn’t mean you’ll notice changes in your thinking, mood, or hunger control that quickly. Brain changes often take longer to become noticeable in daily life. Most people should expect to give a new diet at least 8 to 12 weeks before evaluating whether it’s working for them. Weight loss itself typically becomes visible within 4 to 8 weeks if you’re following the diet consistently.

Want to Apply This Research?

  • Track your diet type (intermittent fasting, Mediterranean, ketogenic, or calorie restriction) alongside your weight and mood scores weekly. Note any changes in mental clarity, focus, or emotional well-being. This helps you see patterns between your diet choice and how you feel, not just how much weight you’ve lost.
  • Instead of just counting calories, choose one specific diet approach (like intermittent fasting or Mediterranean eating) and commit to it for at least 8 weeks. Use the app to log which diet pattern you’re following, track your adherence, and record weekly mood and energy levels. This helps you see if your chosen diet approach is affecting how you feel mentally and physically.
  • Set up weekly check-ins where you rate your mood, mental clarity, and energy levels on a 1-10 scale alongside your weight. Over 8-12 weeks, look for trends in how your chosen diet approach affects these measures. If you’re not seeing improvements in how you feel after 12 weeks, consider trying a different diet approach. Share this data with your healthcare provider to help guide future diet decisions.

This research summary is for educational purposes only and should not be considered medical advice. The findings presented are based on a systematic review of studies with mixed results and important limitations. BDNF changes do not automatically translate to noticeable improvements in brain function or mood. Before starting any new diet or weight-loss program, especially if you have existing health conditions, take medications, have a history of eating disorders, or are pregnant or breastfeeding, consult with your healthcare provider or a registered dietitian. Individual responses to different diets vary greatly, and what works for one person may not work for another. This summary does not replace professional medical guidance.