I recently pulled my IGF-1 (6/2014) from Life Extension Foundation and found that my levels were 175 ng/ml, which was within the lab range of 61-200 ng/ml for my age. (Kudos to Life Extension Foundation and other similar organizations for providing preventative care testing that you'll never get through regular doctors or health insurance!) Now I lift weights and anyone into strength and/or trying to build muscle knows that IGF-1 is good for hypertrophy, i.e. building muscle. So was I happy to be at the top of the range in IGF-1, right? My answer actually is just the opposite: it concerned me a great deal to be that high in IGF-1.
My answer probably made some of you cringe, but I ask the question: how many of you would want high insulin? Well, you should, right? After all, insulin is incredibly anabolic. But, unfortunately, high insulin levels in your middle and senior years will get you killed and I'm 54, so I don't want high insulin either. In any event, this same kind of misguided logic applies to IGF-1: while it is true IGF-1 builds muscle, it also accelerates cancer and causes you to lose your insulin/glucose control.
Now on this page, I am not going to go into why you want to lower IGF-1 if you're over 40 - I will do that on a subsequent page - but let me give you a teaser:
Laron Syndrome. People with Laron Syndrome have a genetic abnormality where they are insensitive to HGH.(human growth hormone). This dramatically lowers their IGF-1 levels and so they all die a painful and early death, right? Wrong! They actually become completely impervious to cancer and diabetes.  Yes, these people are superhuman, because it turns out that losing most of your IGF-1 is a fantasy. Of course, it is probably better if it occurs post-puberty, because those with Laron Syndrome are very short. But imagine living in a world where you do not have to worry about dying a gruesome death from cancer. Such is the world of Laron Syndrome individuals and there have many more health advantages as well: it also looks like lowering IGF-1 is stackin up to be one of the Holy Grails of anti-aging for example.
I should also jump in and point out that this issue is personal for me: I had a high PSA reading (6.3) late in 2013 and they pulled me off of HRT. Yes, that was painful! They then performed a prostate biopsy and left me hanging for 10 days around Christmas waiting for the results - not fun. The good news was that the biopsy revealed no cancer and showed inflammation, so that is probably the root cause of the high PSA. But it is certainly possible I have some prostate cancer, and so I am doing everything in my power to protect myself and so should anyone reading this over the age of 40 in my opinion. Well, actually, you should measure your IGF-1 and see if you are low already of course. But I am on the high side and so want to lower it through natural means.
CAUTION: If you are low or high in IGF-1, discuss with your doctor. There can be medical reasons for being out of range.
Below are some of the Ways to Lower IGF-1 Naturally according to the research. I have recently implemented some of these and will report back with successes and failures. IGF-1 is not the cheapest lab in the world and so it's not something I will be pulling every week though.
1. Decrease Protein. Before I go on, let me say that I have NOT implemented this strategy yet and hope not to. However, I think you read this one, because the underlying principles are important, even though I believe I have discovered a way around it. The fact is, though, that many studies have shown that simply decreasing protein will lower IGF-1 and lower it significantly. So, if you're not an athlete or trying to build muscle, then this is a no brainer in my opinion. Simply drop your protein down to as low as you can do and meet the daily requirements and you should see your IGF-1 levels fall. As an illustration of this, let me relate a story from the health world:
Those of you well-read in health matters will remember that Caloric Restriction (CR or CRON) has been in the forefront of anti-aging strategies for decades, which basically means eating less. It increases maximum life span in many animal species and one of its keys is that it lowers IGF-1. However, it did not work in a human study which was baffling to researchers. However, they figured out the underlying issue: in primates IGF-1 levels do not fall if you cut calories and still consume significant animal protein. Later they found that IGF-1 levels fall significantly if you simply cut out animal protein. (Dr. Greger has a great set of videos on the subject.)
So why do animal proteins uniquely raise IGF-1 levels? The reason is that most animal proteins - whey is the exception - have a high amount of the sulfur-containing amino acid methionine. Researchers have found in animal studies that they can extend maximum life span simply by restricting methionine for this reason, a further verifiction that IGF-1 is one of the roots of all aging. For those of you buying plant protein powders, look at your container: you'll find that a serving has about 300 mg of methionine, a relatively low amount compared to meats and eggs for example.
Now I am trying with all my power to resist this option and have not implemented it. I want to build muscle - aren't we all chasing Dr. Life? - over the years and I'm not going to do it with a meager amount of protein. So I am still consuming 1 gram per pound of body weight, which for me is around 160 grams. I'll explain my strategy for doing that below.
2. Switch to Plant Protein. Anything you can do to lower methionine levels will lower IGF-1 and, as I mentioned above, plant proteins have lower levels of methionine. I just looked at my containers and my rice, hemp and yeast powders all have about 300 mg per serving.
This isn't that big of a change for me, because I was a 95% plant guy anyway. And so I am not sure how much good this will do me. However, some of your reading this could probably significantly lower your IGF-1 with this strategy. In my case, I was eating BPA-free sardines three times a week and whey protein on the animal side of the dietary world and that's it. (Whey protein should not be an issue, but, to play it safe, I cut it out too.)
Note that I still get quite a bit of methionine. My rough back-of-the-envelope calculation for how much methionine I consume each day is about 3 grams. Of course, that's going to be about double what I would get if I implemented a low protein diet, so it's no wonder my IGF-1 is on the high side of the range.
3. Glycine. There is preliminary evidence that supplemental glycine can lower IGF-1 by acclerating the liver clearance of methionine. A recent study on rats showed the same life span extensions by giving them extra glycine as researchers saw with methionine restriction.  Now the researchers gave these animals rather large doses of glycine, something I would not feel comfortable with. But I can see myself taking a few grams of extra glycine each day to help tilt my glycine-to-methionine ratio even more favorably. And all of this is good news, because glycine is readily available as a supplement. Furthermore, a couple of studies show that taking 3 grams of glycine before bed improves sleep. 
There is another more "natural" way to do this as well: increase my intake of plant protein powders with higher levels of glycine. Rice, hemp and yeast have 400, 600 and 800 mg/serving per serving according to my containers. (The total grams of protein per serving are 12, 15 and 13, respectively.) So, obviously, if I emphasize hemp and yeast, I will boost my glycine consumption. This is good, anyway, because rice is so often tainted with traces of arsenic.
NOTE: I prefer Undenatured Proteins, but I can't help but point out that Pea Protein has very low levels (200 mg) of methionine per serving. And, what is more remarkable, is that lysine is 800 mg for the same serving. This gives pea protein an unprecedented 4:1 ratio of glycine to methionine. (One serving is 20 grams of total protein and pea protein will likely lower your blood pressure as well!
CAUTION: Always check with your doctor before taking any new supplement. In addition, keep in mind that there are no studies showing risks from taking extra glycine. Consider this my personal experiment.
4. Intermittent Fasting (Time-Restricted Feeding). IGF-1 is just what its name implies: a growth factor. However, your body has a complementary "system" or mode for recovery. When your body interprets that it's time for recuperation, it will actually lower IGF-1 and other growth factors in order to rebuild and heal itself. And this is exactly what happens when you cut calories or restrict food. The body goes into a state of conservation.
Now it's well-known that intermittent fasting can lower IGF-1, but there are very few studies on the subject. Because of this, many lay people are simply doing it on their own and tracking their IGF-1 and other health paremeters. One of the fairly popular strategies is called 5:2 and involves eating normally five days followed by two days of 600 calories. There are many reports of IGF-1 dropping on this kind of protocol.
One of the techniques used in the animals studies is an 8 hour "feeding window," after which no food is allowed. This technique may lower IGF-1 levels as well.
Unfortunately, there is very little hard info out there and very little published research. Therefore, one has to just try one of the intermittent fasting techniques and see what it does to one IGF-1 levels. I plan on probably trying an 8 or 10 hour daily window method, because I cannot afford to lose much weight. I can eat as much as I need to in those 8 or 10 hours hopefully and then "fast" for the 14 to 16 hours. And I feel I need a method that may trick my body into lowering IGF-1 without weight loss.
6. Folate. Some study work shows that the higher your folate levels, the lower your IGF-1.  However, supplementing with folic acid is unwise in my opinion, because some research shows that it can increase cancer risk. Admittedly, this is controversial, but folate is involved with DNA replication and repair and so potentially it could cause issues. But the bottom line is that you definitely want to make sure that your diet is adequate in folate and that you do not have any digestive issues that could interfere with absorption of nutrients.
7. Resveratrol. This high profile anti-aging supplement has some research showing that it can lower IGF-1 levels.  However, I shy away from it because of a recent animal study that showed that initially resveratrol lowered prostate cancer and then later increased it. You can find the study in my page called A Prostate Cancer Cure?
CAUTION: Interestingly enough, a couple of the pro-inflammatory cytokines, such as IL-6, suppress IGF-1. So you can have the curious where one has high inflammatory promoters and yet low IGF-1. So who wins? Well, recent study work has shown that higher IL-6 and lower IGF-1 is a risk factor for Metabolic Syndrome, or prediabets along with all the nasty health conditions it entails. One summary stated that "IGF-1 has anti-inflammatory effects and decreases expression of proinflammatory cytokines such as interleukin-6 (IL-6). There is also evidence in animal models that IL-6 decreases circulating IGF-1 levels." 
1) Sci Transl Med, Feb 16 2011, 3(70), "Growth Hormone Receptor Deficiency Is Associated with a Major Reduction in Pro-Aging Signaling, Cancer, and Diabetes in Humans"
2) The FASEB Journal, 2011m, 25:528.2, "Dietary glycine supplementation mimics lifespan extension by dietary methionine restriction in Fisher 344 rats"
3) Sleep and Biological Rhythms, Apr 2007, 5(2):126 131, April 2007"Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes"
4) Cancer Prev Res, May 2011, 4:702, "Effects of Tomato- and Soy-Rich Diets on the IGF-I Hormonal Network: A Crossover Study of Postmenopausal Women at High Risk for Breast Cancer"
5) Growth Horm IGF Res, 2013 Dec, 23(6):267-71, "Association between dietary folate intake and serum insulin-like growth factor-1 levels in healthy old women"
6) Nature, 16 November 2006, 444:337-342, "Resveratrol improves health and survival of mice on a high-calorie diet"
7) Diabetes Care, Sep 2008, 31(9):1886 1888, "Reciprocal Association of Plasma IGF-1 and Interleukin-6 Levels With Cardiometabolic Risk Factors in Nondiabetic Subjects"