Macronutrient ratio refers to the ratio of carbohydrates, fats, and proteins in diet. It’s usually expressed as a percentage of total calories coming from each macronutrient.
Bookshelves are full of diet books hyping one ratio over another. However, studies consistently come up with far more mundane results. Setting asides the extremes on both sides, playing around with the macronutrient ratio of your diet seems to have little to no effect on health outcomes.
A 2014 review on the health effects of quantity and quality of carbohydrates summarized the acne-relevant recommendations like this:
For individuals with IR [insulin resistance] or classified as having MetS [metabolic syndrome] or prediabetes, a number of cardiovascular risk factors (i.e., hypertriacylglycerolemia, low HDL-C, hypertension, hyperglycemia) can be significantly improved by the consumption of a diet that is at least moderately restricted in carbohydrate. Thus, for these individuals, a diet that provides 26% to 44% of calories from carbohydrate may be an ideal range in terms of facilitating improvements in cardiovascular risk factors, while at the same time allowing for enough emphasis on high-quality carbohydrate sources to ensure that it also provides a sufficient level of dietary fiber as well as phytochemicals.
Liebman, M. When and why carbohydrate restriction can be a viable option. Nutrition 30, 748–54 (2014). https://www.ncbi.nlm.nih.gov/pubmed/24984988
In other words, people with insulin resistance (includes many people with hormonal-type acne) should moderately restrict carbohydrates and focus on high-quality, unprocessed carbohydrate foods.
The rationale behind this recommendation is that eating a lot of carbohydrates causes the pancreas the pump out insulin. People with insulin resistance already have problems dealing with carbs and eating fewer of them reduces the stress on carbohydrate metabolism.
Meddling with the macronutrient ratio in the diet doesn’t seem to have any effect on systemic inflammation. While not very well studied, a handful of studies has compared the effect of carbohydrate restricted diets to fat restricted diets. None of the studies I found showed any differences between the diets.
For people with hormonal-type acne, it makes sense to restrict carbohydrates to 30 to 40% of total calories. However, this is more of a guideline than a hard and fast rule.
It’s far more important to focus on eating good quality, whole foods than to tinker with the macronutrient ratio.