Nutrition

Low carb, high carb, carnivore: what your diet does to your training.

By Luigi · 4 min read

Clients ask me which diet is best — keto, carnivore, high carb. The honest answer: the label matters far less than three things underneath it. Enough carbs to fuel the session, enough protein to build off it, enough fat to keep your hormones working. Here's what the research shows, and what it means for the diets people ask about.

Carbs: your session's fuel

Muscles store carbohydrate as glycogen, and that store powers hard, repeated effort. In a classic experiment, switching subjects from a fat-and-protein diet to a carbohydrate-rich one swung muscle glycogen from about 0.6 to 4.7 g per 100 g of muscle — and endurance time tracked it almost directly^[1]. That's why the major sports-nutrition position statement sets carbohydrate by how hard you train — roughly 3–5 g/kg a day for light work, up to 6–10 g/kg for hard daily training^[2]. And when researchers took carbs away from elite race walkers for three weeks, their economy got worse and they gained nothing from the same hard training block^[3]. If you train intense — lifting, intervals, sport — chronically low carbs works against your sessions.

Protein: what turns training into muscle

Training is the signal; protein is the material. The largest meta-analysis here — 49 studies, 1,863 people — found protein plus resistance training beat training alone for strength and muscle, with the benefit climbing up to about 1.6 g/kg a day before plateauing^[4]. For an 80 kg person that's roughly 128 g — more than most people eat by accident, and the biggest lever I pull with new clients. The sports-nutrition consensus puts the working range at 1.4–2.0 g/kg/day, spread across your meals^[5]. This is the one macro I keep high whatever style you eat.

Fat: don't cut it to zero

Dietary fat is the raw material your body builds sex hormones from — and that's true for men and women alike. In a 2021 meta-analysis of intervention studies, men who moved to low-fat diets saw total testosterone fall by roughly 10–15% on average^[6]. It shows up in women too: a two-year randomised trial that cut fat to 15% of calories lowered oestradiol by about 20% and progesterone by about 35% versus controls^[9]. None of that is licence to drown everything in oil — but it's a clear reason not to drive fat into the floor chasing "clean eating". A sensible floor of around 0.8–1 g/kg a day keeps the machinery running, whoever you are.

Low carb, high carb — or carnivore?

Everyone wants me to pick a side, and the best evidence won't. In the DIETFITS trial, 609 adults ate either healthy low-fat or healthy low-carb for a year with no calorie target — and both lost about the same (5–6 kg), with no meaningful difference^[7]. What decided results wasn't the ratio; it was who stuck with real food. Low-carb blunts appetite for some; high-carb fuels hard training better. Pick the one you can run for months.

Carnivore comes up a lot. The most-cited study is a survey of 2,029 people who'd eaten all-meat for six months — and it looks rosy: high satisfaction, few complaints^[8]. But it's a self-selected online survey with no control group; people who hated it quit and never filled in the form. It hits protein and fat hard, and cutting processed food helps most people short-term — but it takes carbohydrate near zero, the one macro I don't want gone for anyone training hard. There's no long-term controlled evidence it beats a varied diet.

What I actually tell clients

• Protein first. Around 1.6 g/kg a day, spread across meals^[4]. This is what turns sessions into results.
• Carbs are fuel, not a treat. Put them around your hard sessions. Don't lift or do intervals on empty^[2].
• Don't fear fat to zero. Keep it sensible — your hormones are made from it^[6].
• Pick what you can keep. Low-carb and high-carb both work; adherence decides it^[7].