In this guide
- What intermittent fasting is
- The claims vs the trials
- Fasting and muscle: the real risk
- Fasting and testosterone
- Side effects and who should avoid it
- When intermittent fasting makes sense
- How I would do 16:8 as a man who trains
- My take
Intermittent fasting is everywhere. Men skip breakfast, drink black coffee until lunch and tell you their body is “burning fat as fuel”. Some swear it gave them abs. Others feel terrible and quit after a week.
I am interested in this because my work demands a certain look, plenty of energy and a healthy sex drive at the same time. If a diet makes me lean but tired and flat, it is not a good diet for me. So I went through the trials instead of the testimonials.
I am not a doctor or dietitian, and this is not medical advice. If you have diabetes, take medication, have a history of eating disorders or any medical condition, talk to a professional before you try fasting. The facts here come from Mayo Clinic, the NHS and peer-reviewed research. The opinions are mine.
What intermittent fasting is
Mayo Clinic describes intermittent fasting as a pattern of eating based on time limits: you eat normally for a set period, then switch to very few or no calories (Mayo Clinic: intermittent fasting). The main types:
- Time-restricted eating (16:8, 18:6, etc.): you eat within a daily window, for example 8 hours, and fast for the rest.
- 5:2: you eat normally five days a week and eat very little on two days.
- Alternate-day fasting: fasting or eating very little every other day.
16:8 is by far the most popular with men, mostly because it means skipping breakfast.
The claims vs the trials
The popular claims are that fasting “switches on” fat burning, boosts metabolism and works better than counting calories. A 2019 review in the New England Journal of Medicine described real biological effects of fasting periods, like metabolic switching from glucose to ketones, and many promising results in animals (de Cabo and Mattson, PubMed). But for fat loss in humans, the important question is simple: does it beat a normal diet with the same calories?
The NEJM 2022 trial. 139 adults with obesity were randomised to calorie restriction (1,500 to 1,800 kcal a day for men) with or without an 8-hour eating window, for 12 months. Weight loss was 8.0 kg with time-restricted eating and 6.3 kg without it, a difference that was not statistically significant. Body fat, waist and metabolic risk factors were also similar (Liu et al., PubMed).
The TREAT trial, 2020. 116 adults with overweight or obesity, about 60 percent of them men, were assigned to 16:8 eating or three meals a day, with no other diet advice. After 12 weeks, the 16:8 group lost about 0.94 kg, the control group about 0.68 kg, and the difference between groups was not significant. The authors concluded that time-restricted eating, without other changes, was not more effective than eating throughout the day (Lowe et al., PubMed).
Mayo Clinic summarises it well: intermittent fasting may improve weight, blood sugar, cholesterol, blood pressure and inflammation in the short term, but the long-term effects are not clear, and some studies find that simply limiting calories may have the same benefit.
Intermittent fasting is not magic. It is a calorie-control tool that suits some men and not others.
Fasting and muscle: the real risk
This is the point most fasting fans ignore. In the TREAT trial, the group that did 16:8 without other changes lost more lean mass than the control group (Lowe et al., PubMed). That is bad news if you want to look athletic.
But context matters. In a 2016 study, 34 resistance-trained men did eight weeks of either a normal diet or 16:8 eating while continuing to lift. The 16:8 group lost fat while keeping fat-free mass and maximal strength (Moro et al., PubMed).
The difference is obvious: training and protein. If you fast, lift weights and hit your protein target in a shorter window. My guide on how much protein to build muscle explains how much you need, and the strength training plan for beginners gives you the training side.
Fasting and testosterone
Here is something you will not hear from fasting influencers. In the same 2016 study, testosterone and IGF-1 decreased significantly in the 16:8 group, with no changes in the normal-diet group (Moro et al., PubMed). The men still kept their muscle and strength over eight weeks, and this was a small, short study, so I would not panic. But it does contradict the idea that fasting “boosts” testosterone.
Any significant calorie deficit, especially combined with hard training and poor sleep, can affect energy, mood and libido. If you notice your sex drive drop while dieting, that is a signal to eat a bit more, sleep more or train a bit less. Read testosterone and sex drive and low libido in men for the bigger picture.
Side effects and who should avoid it
Mayo Clinic notes that intermittent fasting may make people feel very tired and dizzy, can affect diabetes management, and can cause headaches, mood swings and constipation. It also says fasting may not be a healthy pattern for people who:
- Have an eating disorder.
- Are pregnant or breastfeeding.
- Are at high risk of bone loss and falls.
Mayo also mentions that some evidence suggests a 16:8 cycle may raise heart disease risk compared with other time-restricted cycles. That evidence is early and debated, but it is another reason not to treat fasting as automatically healthy.
If you have ever had a difficult relationship with food, binge eating or extreme dieting, rigid fasting rules can make it worse. The NHS has information and support on eating disorders, which affect men too.
When intermittent fasting makes sense
Fasting is a tool. It can make sense if:
- You are not hungry in the morning and breakfast is a habit, not a need.
- You snack at night and a fixed cut-off time helps you stop.
- You like fewer, bigger meals and they keep you full.
- It simplifies your day and you can still hit your protein.
It probably does not make sense if you train hard early in the morning on an empty stomach and feel weak, if you get irritable and overeat later, if you have a medical condition that needs regular meals, or if it is ruining your social life.
How I would do 16:8 as a man who trains
If I wanted to try intermittent fasting for a leaner body, this is how I would set it up:
- Pick a window that fits your life, for example 12:00 to 20:00. Train inside or near the window if you can.
- Keep calories controlled. A window does not cancel the energy balance. A moderate deficit is still the engine.
- Hit your protein in two or three meals: around 1.6 to 2.2 g per kg of bodyweight is a practical target for most men who lift.
- Eat real food: protein, vegetables, fruit, whole grains, potatoes or rice, healthy fats. The NHS guide to eating a balanced diet is a good base.
- Drink plenty of water during the fast. Black coffee and tea are fine for most people. See how much water should a man drink.
- Keep lifting two to four times a week to protect muscle.
- Protect sleep. Do not eat a huge meal right before bed. Read how much sleep do men need.
- Track your waist, strength and energy. If strength drops, libido drops or you feel awful, change the plan.
If you are trying to lose belly fat, fasting is optional. The foundations are the same, as I explain in how to lose belly fat.
My take
Intermittent fasting is not a scam, but it is not the miracle it is sold as either. The best trials show it works about as well as normal calorie restriction, no better. Its real value is practical: for some men, a clear eating window makes it easier to eat less.
If that is you, use it, but protect your muscle with lifting and protein, and listen to your body, especially your energy and sex drive. If fasting makes you miserable, eat breakfast and control your calories in a way you enjoy. The best diet is the one you can stick to while still training hard and living well.
If you want the human stories of the women of this industry, read my columns on House of Maximo. Follow my work at maximogarciaworld.com, and for the 18+ side, fuckingpornstars.net.
Sources
- Mayo Clinic. Intermittent fasting: What are the benefits?
- Liu D et al. Calorie restriction with or without time-restricted eating in weight loss. New England Journal of Medicine, 2022.
- Lowe DA et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Internal Medicine, 2020.
- Moro T et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine, 2016.
- de Cabo R, Mattson MP. Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine, 2019.
- NHS. Eating disorders.
- NHS. Eating a balanced diet.
