Dietary Fat Calculator
Keep fat at 20–35% of calories, or at least 0.5 g per kg of body weight. Below that is where the evidence on low-fat diets and hormones starts to matter.
Your results
General nutrition information, not a prescriptive meal plan. If you have a medical condition affecting your diet, are pregnant, or have a history of disordered eating, speak to a doctor or a registered dietitian.
The low-fat and testosterone question, honestly
A 2021 systematic review and meta-analysis of six controlled trials found that when men switched from around 40% of calories from fat to around 20%, testosterone fell by 10–15% on average.
The honest complication: a more recent meta-analysis on the same question found no clear effect. This is a genuinely unsettled literature with a small number of small studies, and anyone presenting either result as definitive is overstating it.
Which makes the sensible reading: there may be a modest effect at the low end, so do not eat a very low-fat diet. That is a cheap precaution against an uncertain risk. It is not a reason to eat high fat deliberately — beyond about 30% of calories there is no evidence of further benefit, and it costs you carbohydrate you could be training on.
For context on size: a week of five-hour nights reduces testosterone by more than this dietary change does.
Fat quality, which matters for different reasons
The hormonal question is about total fat. Fat type matters for cardiovascular health, which is the longer-horizon and arguably more important concern.
- Monounsaturated — olive oil, avocado, nuts. Make these the bulk.
- Omega-3 — oily fish twice a week, or an algae supplement if you do not eat fish.
- Saturated — not to be eliminated; current guidance is under about 10% of calories.
- Industrial trans fats — avoid entirely where they still exist.
For women, the risk at the low end shows up as menstrual disruption rather than a hormone number — and it usually reflects low total energy rather than low fat specifically. If your cycle changes during a diet, that is a reason to raise calories.
Common questions
How much fat should I eat per day?
20–35% of calories, and at least 0.5 g per kg of body weight.
Will eating more fat raise my testosterone?
Only if you were eating very little. Beyond about 30% of calories there is no evidence of further benefit.
Should I cut fat or carbs to lose weight?
Whichever you find easier to sustain, keeping fat above the floor.
Is a very low fat diet bad?
Below about 15% of calories is where problems start appearing. There is no good reason to go there.
Related calculators
Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
