Somewhere in your forties, things start to shift. You train the same way but recover more slowly. The belt gets a notch tighter even though you’re not eating more. Afternoon energy dips are now a daily event, and motivation isn’t what it used to be.
Many men put this down to “just getting older” and quietly accept it. Others jump straight to testosterone boosters or online clinics. The truth sits in between: some change is normal, but a lot of what men feel after 40 is strongly influenced by how they eat, sleep, move and drink. And that is good news, because those are things you can change.
In this guide I’ll walk you through what actually happens to men’s bodies after 40, what the research says about nutrition and testosterone, and the practical steps that make the biggest difference.
What changes in men’s bodies after 40?
Testosterone declines gradually. From around 40, testosterone tends to fall slowly, often cited at around 1% per year. Large studies also show that testosterone levels in men have dropped at a population level over recent decades, independent of age, which points strongly to lifestyle factors like body weight and general health.
True “low T” is less common than you’d think. A large European study of men aged 40 to 79 found that late-onset hypogonadism, meaning low testosterone combined with clear symptoms like low libido, reduced morning erections and erectile problems, affected only around 2% of men. Many men with low energy have normal testosterone, and the cause lies elsewhere: poor sleep, stress, excess weight, blood sugar swings or nutrient gaps.
Muscle is harder to keep. Without strength training and enough protein, men gradually lose muscle mass from midlife. Less muscle means a slower metabolism, less strength and a greater tendency to gain fat.
Fat moves to the middle. Weight gain after 40 often shows up as belly fat (visceral fat). This type of fat is metabolically active, linked to insulin resistance and heart disease, and it also converts testosterone into oestrogen. That creates a loop: more belly fat, lower testosterone, easier fat gain.
The biggest lever: body weight
If you’re carrying extra weight around the middle, losing it is probably the single most effective natural way to support your testosterone. A meta-analysis found that weight loss, whether through diet or surgery, significantly increased testosterone levels in men with obesity, and the more weight lost, the bigger the rise.
This is not about crash diets. Very aggressive calorie restriction can actually lower testosterone and cost you muscle. A steady approach of around 0.5 to 1 kg per week, built around protein, vegetables and whole foods, works far better and lasts.
Nutrition for testosterone and energy: what really matters
1. Eat enough protein, spread over the day
Protein protects muscle, keeps you full and helps with weight management. Research on resistance training shows muscle gains plateau at around 1.6 g of protein per kg of body weight per day. For an 85 kg man, that’s roughly 135 g a day, or about 30 to 40 g per meal.
Good sources: eggs, fish, chicken, Greek yoghurt, lentils, chickpeas, tofu and lean meat.
2. Don’t go too low on fat
Your body makes testosterone from cholesterol, so very low-fat diets aren’t your friend here. A meta-analysis of intervention studies found that men on low-fat diets had modestly lower testosterone than those on higher-fat diets.
Focus on quality fats: extra virgin olive oil, nuts, seeds, avocado and oily fish like salmon, sardines and mackerel.
3. Cover key nutrients: zinc and vitamin D
Zinc plays a direct role in testosterone production, and deficiency is linked to lower levels. You’ll find it in shellfish, red meat, pumpkin seeds, eggs and legumes.
Vitamin D is another one to watch. In one trial, men with low vitamin D who took a supplement for a year saw their testosterone increase compared to placebo. Even in sunny Barcelona, many people who work indoors have low levels. A simple blood test tells you where you stand.
Supplements only help if you’re actually low. More is not better.
4. Follow a Mediterranean-style pattern
The Mediterranean diet is one of the best-researched eating patterns for heart health, and that matters more than ever after 40. Good blood flow also matters for sexual health: in one trial, men with obesity who followed a Mediterranean-style diet and exercised more saw significant improvements in erectile function within two years.
If you want a practical starting point, my Mediterranean Diet Guide includes a food list and a 7-day meal plan.
5. Watch alcohol
Regular heavier drinking disrupts sleep, adds empty calories and can lower testosterone. You don’t need to stop completely, but keeping alcohol to a few drinks a week, and not most evenings, makes a noticeable difference to energy and weight.
Mario's practical tip
Protect your sleep for one week and see what changes. Just one week of 5-hour nights can lower testosterone by 10 to 15%. For the next 7 days, set a fixed bedtime that gives you at least 7.5 hours in bed, stop alcohol 3 hours before sleep, and leave your phone outside the bedroom. Notice your energy, mood and cravings by day 5. Most men are surprised how much changes.
Sleep: the overlooked testosterone booster
Most testosterone is released during sleep. In one study, healthy young men who slept just 5 hours a night for a week saw daytime testosterone drop by 10 to 15%, roughly the equivalent of ageing 10 to 15 years.
If you regularly sleep less than 7 hours, fixing that may do more for your energy and hormones than any supplement. I’ve shared the most practical lessons in Why We Sleep: Practical Lessons from Matthew Walker.
Training: lift something heavy
Strength training two to three times a week is essential after 40. It preserves muscle, improves insulin sensitivity, supports bone health and helps with body composition. Combine it with regular walking and some cardio, and you’ve covered most of the bases.
What about supplements?
Most “testosterone booster” products have little solid evidence behind them, and some contain ingredients you’d rather not take. A few supplements are well researched and genuinely useful for active men over 40:
Creatine supports strength, muscle and possibly brain health, and becomes even more relevant as we age. Read more in Creatine: Benefits, Dosage, Brain Health & Side Effects.
Vitamin D if your levels are low.
Omega-3 if you rarely eat oily fish.
For a wider overview, see The 5 Sports Supplements That Actually Deserve Your Money.
A simple day of eating for men over 40
Breakfast: 3 eggs with spinach and tomatoes, wholegrain toast with olive oil
Lunch: Grilled salmon or chicken, a large salad with chickpeas, olive oil and lemon
Snack: Greek yoghurt with berries and a handful of walnuts or pumpkin seeds
Dinner: Lentil and vegetable stew, or lean meat with roasted vegetables and potatoes
Drinks: Water through the day, coffee before early afternoon, alcohol kept for the weekend
When to see a doctor
Please speak with your GP if you have low libido, erectile problems, persistent fatigue, low mood, loss of muscle or unexplained weight changes. A blood test for testosterone (ideally taken in the morning), along with vitamin D, blood sugar, thyroid and cholesterol, gives a much clearer picture than guessing.
How I can help
Many men I work with tell me the same thing: they knew something wasn’t right, but didn’t know who to ask. A doctor checks for disease, a personal trainer focuses on workouts, but nobody looks at the full picture of food, sleep, stress, energy and hormones together.
That’s exactly what I do. In my Men’s Health programme, we look at your symptoms, lifestyle and, where useful, your blood results. Then we build a realistic plan that fits your work, family and training, so you get your energy back, lose the belly fat and feel like yourself again.
I work with men in Barcelona and online, in English and German.
Ready to take the first step? Book a free 20-minute call and we’ll talk through where you are and what would help most.
FAQ
Does testosterone drop after 40?
Yes, testosterone tends to decline gradually from around 40, often cited at about 1% per year. However, true low testosterone with symptoms affects only around 2% of men aged 40 to 79. Many men with low energy have normal levels, and the cause is often sleep, weight, stress or nutrition.
Can diet increase testosterone naturally?
Diet can support healthy testosterone levels, especially through weight loss if you carry extra belly fat, enough healthy fats, and good zinc and vitamin D status. Food won't push testosterone above your natural range, but it can help you avoid the drops caused by excess weight, deficiencies and poor sleep.
Why is it harder to lose weight after 40 for men?
Muscle mass declines with age if you don't train for it, which lowers your metabolism. Sleep, stress, alcohol and a busier life also play a role. Strength training, enough protein and regular meal patterns are the most effective ways to turn this around.
How much protein do men over 40 need?
For active men who strength train, around 1.6 g of protein per kg of body weight per day is a good target. For an 85 kg man, that is about 135 g a day, ideally spread over three to four meals of 30 to 40 g each.
Do testosterone booster supplements work?
Most testosterone booster products have little reliable evidence behind them. Correcting a real deficiency, such as low vitamin D or zinc, can help. Creatine and omega-3 are well researched for muscle and overall health. Always check with a professional before starting new supplements.
Does semen retention boost testosterone?
There's little evidence for this. One small study found testosterone peaked around day 7 of abstinence, then returned to normal levels, so any effect appears small and short-lived. In fact, a large study of more than 30,000 men found that those who ejaculated more often had a lower risk of prostate cancer. Some yoga and spiritual traditions value conserving sexual energy, but for testosterone and vitality, sleep, body weight, training and nutrition matter far more.
When should I get my testosterone tested?
Speak with your GP if you have low libido, erectile problems, ongoing fatigue, low mood or loss of muscle. Testosterone should be tested in the morning, ideally alongside vitamin D, blood sugar, thyroid and cholesterol for a full picture.
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