Most fitness advice assumes everyone responds to training and nutrition the same way. In reality, people begin from very different physical starting points. Your body composition affects how easily you gain muscle, lose fat, recover from training, and even how your metabolism behaves day to day. That means the best strategy for building muscle or losing fat depends heavily on your current physique and body composition.
In this video, Jeremy Ethier breaks down the most common body type categories, explains how to determine where you fit, and looks at how modern body composition testing compares to older somatotype ideas. He also covers one of the most searched fitness questions today: how to fix the skinny fat physique and why the solution is often simpler than people think.
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Men and women with very different physiques underwent DXA scans, strength testing, and doubly labeled water testing to measure real world calorie expenditure and intake. From the data, four major starting body type categories emerged: skinny, skinny fat, bulky, and high body fat.
The skinny body type is lean, lightweight, and low in overall muscle mass. Aaron fit this category well. He was lean at 13% body fat, but still carried below average muscle mass. Maria weighed just 97 pounds and wanted to feel stronger, especially in her upper body. Her low muscle mass was not only affecting performance. Her bone density also ranked lower than 72% of women her age.
The skinny fat category often looks relatively normal in clothing, but underneath there is a higher body fat percentage combined with low muscle mass, particularly around the waist and lower abdomen. This body type is extremely common because most adults gradually gain one to two pounds per year, and without proper resistance training, much of that gain comes from fat rather than muscle. Every participant in this category also had below average muscle mass. Fortunately, fixing the skinny fat physique is usually straightforward once training and nutrition are aligned properly.
The bulky body type carries above average muscle mass, but also enough body fat to hide muscular definition. Sahil and Eric both fit this category well. Eric’s FFMI was close to the natural ceiling for muscularity, yet both men were still in the upper twenties for body fat percentage. Melody showed a similar trend after five years of lifting. She had already built substantial muscle mass, but at that stage a focused fat loss phase made more sense than continuing to bulk.
The final category was high body fat, defined here as above 30% body fat for men and above 40% for women. AJ and Michelle both fell into this group. Despite not strength training consistently, both actually carried more muscle than several leaner participants. However, the excess body fat made movement more difficult and came with more obvious long term health concerns. This is also where traditional somatotype labels become less useful than direct body composition measurements.
One of the most surprising findings was that none of the participants had an unusually fast or slow metabolism. Aaron’s resting metabolic rate was only around 1,500 calories per day, which was completely normal for his body size. However, his physical activity burned an additional 2,700 calories daily, bringing his total expenditure above 4,200 calories per day. That explained why he could eat far more food than AJ despite weighing much less.
Maria remained skinny for a different reason. Her daily calorie intake of roughly 2,080 calories closely matched her estimated needs, suggesting she naturally regulated her food intake well without overeating.
Major Trends
Two major trends appeared in the skinny fat group. First, calorie intake was consistently underestimated. Second, resistance training was either inconsistent or ineffective. The bulky group showed much higher calorie expenditure overall. Sahil and Melody both burned more than 3,000 calories daily due to higher muscle mass and activity levels. Muscle tissue is metabolically active, with each additional pound burning roughly 10 calories per day at rest. However, that advantage disappeared when calorie intake was underestimated. Melody believed she was eating between 1,800 and 2,200 calories daily, but testing showed her true intake was closer to 3,300 calories.
In the high body fat group, calorie intake once again outweighed metabolic differences. Michelle consumed nearly 3,900 calories per day, while AJ underestimated his intake by almost 800 calories daily. Two additional factors became more noticeable in this category: subconscious movement levels, which vary dramatically between individuals, and the brain’s reward response to food, which may influence hunger, fullness, and overeating behavior.
The best training and nutrition strategy changed significantly depending on the starting point.
Advice for Different Body Types
Skinny individuals generally benefit most from a slight calorie surplus combined with three well structured full body workouts each week. The primary goal is building muscle mass gradually while improving overall strength.
Skinny fat individuals are often ideal candidates for body recomposition, meaning they can lose fat and gain muscle at the same time. In most cases, the best approach includes progressive strength training, a small calorie deficit, and higher protein intake to support muscle growth while reducing fat mass.
Bulky body types usually do not need a dramatically different training plan. More often, they benefit from improved food tracking, better nutritional consistency, and a moderate calorie deficit to reveal the muscle they have already built.
For individuals with high body fat levels, the biggest priorities are usually sustainable habits, increased daily activity, nutritional awareness, and having a strong personal reason for change that supports long term consistency.
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