[Experiment] Complete Body Type Prompt Guide | 24 Conditions, 72 Images from slim to bbw

Conclusions First

Control in the larger direction is strong. Slimmer direction barely works. The same asymmetry as “increase > decrease” confirmed in the areola experiment was reproduced for body type.

Effective Prompts (Larger Direction)

Word	Effect	Use
bbw	★★★ Maximum	Major weight gain
fat	★★★ Large	Clearly heavy build
chubby	★★☆ Large	Pudgy (with belly sag)
curvy	★★☆ Medium	Chubby with waist maintained
muscular	★★★ Large	Muscular ※ Risk of subject identity collapse (ethnicity/hairstyle may change)

Ineffective Prompts

Slimmer direction: slim, slender, thin, petite are nearly the same as control. Only skinny has moderate effect
Compound body type descriptions: hourglass figure, pear-shaped body, wide hips narrow waist all show no effect
Height specification: tall 175cm, short 150cm don’t function as height control (short causes short hair instead)

Experiment Design

Parameter	Value
Model	z-image-turbo (6B, photorealistic distillation)
Steps	8
CFG	1.0
Size	1024x1024
Seeds	3 fixed (shared across all conditions)
Total	24 conditions × 3 seeds = 72 images

Base Prompt

1girl, 32yo japanese actress, {VARIABLE}, white bikini, full body, standing, simple white background, soft studio lighting

Using full body + white bikini for clear full-body body type observation.

A. Control

seed 1	seed 2	seed 3

Standard to slightly slim build. Light waist. This is the baseline.

B. Slimmer Direction

Condition	seed 1	seed 2	seed 3	Effect
slim				★☆☆ Small
slender				★☆☆ Small
petite				☆☆☆ None
skinny				★★☆ Medium
thin				★☆☆ Small

Only skinny has moderate effect. Consistently thinner limbs and narrower waist width observed. Others are nearly the same as control. The control itself is a slightly slim build, which may be creating a ceiling effect limiting the range of change toward slimmer.

C. Toned Direction

Condition	seed 1	seed 2	seed 3	Effect
athletic				★☆☆ Slight ab lines
fit body				☆☆☆ None
toned body				☆☆☆ None
muscular				★★★ Large (major side effects)

muscular is powerful but risky. Abdominal muscle lines and increased limb muscle mass confirmed across all seeds. However, seed 1 shows a complete change in skin tone and facial features, causing a critical side effect of subject identity collapse.

fit / toned show almost zero body effect. High heels appeared as a common side effect across Group C.

D. Larger Direction

Condition	seed 1	seed 2	seed 3	Effect
curvy				★★☆ Gentle
thick				★★☆ Medium–Large
plump				★★☆ Medium–Large
chubby				★★★ Large
fat				★★★ Large
voluptuous				★★☆ Medium
bbw				★★★ Maximum

Larger Size Ranking

bbw >= fat > chubby > thick >= plump > curvy >= voluptuous

Lab Director Comment: Of course bbw is the maximum — that tracks. I’m a fan of curvy girls so this ranking is very welcome.

Stage	Recommended Word	Waist	Abdomen
Gently fuller	`curvy`	Maintained	Flat
Medium	`plump` / `thick`	Weakened	Gains thickness
Clearly heavy	`chubby`	Nearly gone	Sag appears
Major weight gain	`fat` / `bbw`	Gone	Protruding forward

Side effects: Long dresses may appear with thick / voluptuous / fat.

E. Compound Body Type Descriptions

Condition	seed 1	seed 2	seed 3	Effect
hourglass figure				☆☆☆ Minimal
pear-shaped body				☆☆☆ None (tattoo appeared)
wide hips, narrow waist				☆☆☆ None
long legs				☆☆☆ Only heel triggering
short and compact body				☆☆☆ None

Compound body type descriptions completely failed. Only hourglass figure shows a slight waist emphasis. pear-shaped body caused a tattoo side effect. Compared to single adjectives (Group D), compound descriptions have significantly weaker influence on the model.

F. Height

Condition	seed 1	seed 2	seed 3	Effect
tall, 175cm				★☆☆ Slightly more elongated
short, 150cm				☆☆☆ Short hair instead

Height numerical values don’t work. short caused short hair in all 3 images — strongly interpreted as a hair style token. tall creates a slightly elongated impression, but as a slimming byproduct rather than height control.

All Conditions Summary

Condition	Body Change	Stability	Side Effects	Recommendation
slim	★☆☆	Stable	Small	△
slender	★☆☆	Stable	Small	△
petite	☆☆☆	—	Background interference	×
skinny	★★☆	Stable	Composition change	◯ Best for slim
thin	★☆☆	Stable	Small	△
athletic	★☆☆	Unstable	High heels	△
fit body	☆☆☆	—	High heels	×
toned body	☆☆☆	—	High heels	×
muscular	★★★	Stable	Ethnicity change	△ Caution
curvy	★★☆	Stable	Small	◎ Gentle fuller
thick	★★☆	Stable	Dress appearance	◯
plump	★★☆	Stable	Small	◯
chubby	★★★	Stable	Small	◎
fat	★★★	Stable	Dress appearance	◯
voluptuous	★★☆	Stable	Dress appearance	△
bbw	★★★	Stable	Small	◎ Maximum
hourglass	☆☆☆	—	Composition change	×
pear-shaped	☆☆☆	—	Tattoo	×
wide hips	☆☆☆	—	Small	×
long legs	☆☆☆	—	Heels	×
short compact	☆☆☆	—	Dress	×
tall 175cm	★☆☆	Unstable	Multiple people	×
short 150cm	☆☆☆	—	Short hair	×

Practical Recommendations

Larger Direction (by stage)

Gently Fuller

curvy

Chubby

chubby

Maximum

bbw

Slimmer Direction

Slim (Only Option)

skinny

Effect is moderate. Change range is limited since the default is already slightly slim.

What to Skip

fit / toned don’t work — no toning effect; only heels appear
Compound body type descriptions (hourglass, etc.) all failed — use single adjectives instead
Numeric height specifications don’t work — short causes short hair
muscular carries ethnicity change risk — accept the possibility of subject identity collapse

Lab Director Comment: Larger direction works, slimmer barely does — same asymmetry as breast size. The “increase > decrease” pattern seems consistent for body type too. short causing short hair is a complete trap.

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