For the record, berberine can increase SHBG without diet or exercise. It does so regularly in studies of women with metabolic disorders.
A researcher friend of mine with low SHBG began to incorporate berberine and milk thistle into his TRT regimen, and was able to increase his SHBG up to 28 from 14 nmol/L. This effect took approximately 65 days, and persisted even after he stopped berberine. He made no other life changes.
Of course, there's something to be said for diet and exercise, but we have to understand one thing before we beat ourselves to death about lifestyle: it should really have very little to do with SHBG.
The average SHBG is 35 nmol/L for males. That includes people who don't lift weights, run or eat well. This number comes from the same study that suggests 650 ng/dL as the average male total testosterone.
SHBG also increases, not decreases, with age. A damaged liver, such as a liver with cirrhosis, will produce elevated SHBG. As will an iron overload. This is contrary to a lifestyle and diet focused approach to SHBG management.
We with low SHBG have a very specific metabolic disorder that limits the types of abuses our bodies can endure. So, yes, we ought to tread carefully around fructose and monosaccharides and should probably stay active and keep our metabolisms high.
Berberine is able to activate an enzyme called Adenosine Monophosphate-Activated Protein Kinase (AMPK) while inhibiting Protein-Tyrosine Phosphatase 1B (PTP1B). Activating AMPK is important to health, and appears to play a key role in reversing insulin resistance, promoting glycolysis, and reducing oxidative stress. One result of activating AMPK is suppression of hepatic glucose output, so that insulin and IGF-1 levels are lower. Both berberine and metformin, (as mentioned previously, the drug commonly used for diabetes and PCOS), activate AMPK.
Berberine has another action that metformin does not: it blocks proprotein convertase subtilisin kexin 9 (PCSK9), which plays a key role in metabolism of lipoprotein. Some people overexpress PCSK9 because of a genetic variant, and berberine helps lower their LDL particles by 10 to 32 percent
It would seem that our genetic disorder relates to some of the things that berberine corrects, including the overexpression of PCSK9 or an issue with AMPK expression.
So, while it is nice to say "no pill will replace hard work", the reality is that no hard work will inhibit PCSK9 or activate AMPK. So, the supplements are probably more necessary than the training.
It's kind of like someone telling a man with primary hypogonadism that diet, exercise and sleep will correct his low testosterone. If your testes don't respond to LH, nothing other medicine will help. If your hypothalamus doesn't work properly, it doesn't give a rat's ass about your gym time or diet. Such can be the case with a bad liver and low SHBG.