Skipping meals isn’t just a fad anymore—intermittent fasting (IF) has gone from buzzword to lifestyle for millions. But what does science really say about it? Dr Sudhir Kumar, a CMC Vellore–trained neurologist, decided to break it down on X, cutting through the hype with a no-nonsense summary. His take: yes, fasting works, but not always for the reasons people think. And it definitely comes with caveats.
When it comes to blood pressure, the doctor says results are modest at best. Some studies show a small dip in systolic and diastolic numbers, but most of the improvement is linked to weight loss, not fasting alone. Cholesterol, however, fares better—many people see a drop in total and LDL cholesterol, especially if they’re overweight or obese.
Effects on brain
The brain angle is where things get really interesting. Animal studies suggest fasting boosts brain-derived neurotrophic factor (BDNF), which supports neuroplasticity, learning, and memory. Early human research hints at similar effects, but the evidence isn’t strong enough yet to call it a proven brain hack.
Gut health
Fasting does shake things up, with noticeable changes in the microbiome, but the patterns are all over the place. There’s no single “healthy” fasting microbiome that fits everyone. What does seem consistent, though, is reduced inflammation. Many studies show a fall in markers like CRP, again tied partly to losing weight.
Bonus benefits
Improved insulin sensitivity, better glucose control, smaller waistlines, and, of course, weight loss. But Dr. Kumar reminds people that fasting isn’t for everyone. Pregnant or breastfeeding women, those with eating disorders, unstable diabetes, or frail elderly adults should stay away unless guided by a doctor.
The real kicker? Most of the benefits aren’t because of some magical fasting window—they come from eating fewer calories overall. Whether you’re doing time-restricted eating, alternate-day fasting, or the 5:2 plan, results differ depending on your body, health, and how long you stick with it.
What Harvard researchers say
Intermittent fasting may be just as effective as traditional calorie restriction (CR) for weight loss and improving cardiometabolic health, according to new research published in The BMJ.
The study, led by a postdoctoral research fellow at Harvard T.H. Chan School of Public Health, and co-authored by Frank Hu, Professor of Nutrition and Epidemiology, is the largest systematic review to date on intermittent fasting. Researchers analysed 99 randomised clinical trials involving more than 6,500 participants, most of whom were overweight or living with health conditions such as diabetes and hypertension. The average body mass index (BMI) was 31.
Three main intermittent methods were assessed: time-restricted eating (e.g., the 16:8 plan), whole-day fasting (e.g., the 5:2 diet), and alternate-day fasting (ADF), in which individuals abstain from food every other day. Compared with unrestricted diets, both IF and CR led to modest weight loss. However, ADF stood out, resulting in an additional 1.3 kilograms of weight loss compared to CR. It also showed improvements in waist circumference, cholesterol, triglycerides, and C-reactive protein—an inflammation marker linked to cardiovascular risk.
Despite these encouraging results, the researchers cautioned that most trials lasted less than 24 weeks, leaving questions about long-term health effects unanswered. They emphasised that intermittent fasting should not be viewed as a universal solution.
The findings suggest that intermittent fasting, particularly alternate-day fasting, may offer a viable alternative to calorie restriction, but more extended studies are needed to confirm its sustainability and long-term benefits.
When it comes to blood pressure, the doctor says results are modest at best. Some studies show a small dip in systolic and diastolic numbers, but most of the improvement is linked to weight loss, not fasting alone. Cholesterol, however, fares better—many people see a drop in total and LDL cholesterol, especially if they’re overweight or obese.
Effects on brain
The brain angle is where things get really interesting. Animal studies suggest fasting boosts brain-derived neurotrophic factor (BDNF), which supports neuroplasticity, learning, and memory. Early human research hints at similar effects, but the evidence isn’t strong enough yet to call it a proven brain hack.
✅Intermittent fasting (IF): What the evidence actually shows (quick summary)
— Dr Sudhir Kumar MD DM (@hyderabaddoctor) September 19, 2025
1. Blood pressure: Modest, inconsistent reductions.
Some trials report small falls in systolic/diastolic BP, especially when fasting causes weight loss.
2. Cholesterol / non-HDL cholesterol: Often…
Gut health
Fasting does shake things up, with noticeable changes in the microbiome, but the patterns are all over the place. There’s no single “healthy” fasting microbiome that fits everyone. What does seem consistent, though, is reduced inflammation. Many studies show a fall in markers like CRP, again tied partly to losing weight.
Bonus benefits
Improved insulin sensitivity, better glucose control, smaller waistlines, and, of course, weight loss. But Dr. Kumar reminds people that fasting isn’t for everyone. Pregnant or breastfeeding women, those with eating disorders, unstable diabetes, or frail elderly adults should stay away unless guided by a doctor.
The real kicker? Most of the benefits aren’t because of some magical fasting window—they come from eating fewer calories overall. Whether you’re doing time-restricted eating, alternate-day fasting, or the 5:2 plan, results differ depending on your body, health, and how long you stick with it.
What Harvard researchers say
Intermittent fasting may be just as effective as traditional calorie restriction (CR) for weight loss and improving cardiometabolic health, according to new research published in The BMJ.
The study, led by a postdoctoral research fellow at Harvard T.H. Chan School of Public Health, and co-authored by Frank Hu, Professor of Nutrition and Epidemiology, is the largest systematic review to date on intermittent fasting. Researchers analysed 99 randomised clinical trials involving more than 6,500 participants, most of whom were overweight or living with health conditions such as diabetes and hypertension. The average body mass index (BMI) was 31.
Three main intermittent methods were assessed: time-restricted eating (e.g., the 16:8 plan), whole-day fasting (e.g., the 5:2 diet), and alternate-day fasting (ADF), in which individuals abstain from food every other day. Compared with unrestricted diets, both IF and CR led to modest weight loss. However, ADF stood out, resulting in an additional 1.3 kilograms of weight loss compared to CR. It also showed improvements in waist circumference, cholesterol, triglycerides, and C-reactive protein—an inflammation marker linked to cardiovascular risk.
Despite these encouraging results, the researchers cautioned that most trials lasted less than 24 weeks, leaving questions about long-term health effects unanswered. They emphasised that intermittent fasting should not be viewed as a universal solution.
The findings suggest that intermittent fasting, particularly alternate-day fasting, may offer a viable alternative to calorie restriction, but more extended studies are needed to confirm its sustainability and long-term benefits.
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