Yes, nitric oxide is just as important as testosterone as far as how you feel and your ability to avoid chronic disease. And, yes, significant saturated fat lowers nitric oxide. Yet, when I tell most men on the Peak Testosterone Forum that any significant amount of saturated fat will lower nitric oxide, I can tell that they usually don’t believe me. This always shocks me, because there is such a huge body of research that shows this fact. Below I will show you study after study that demonstrates that higher saturated fat meals not only lowers nitric oxide but also lower blood flow and endothelial function as well (of course).
I always get the same objections:
“That’s not right: I can get an erection just fine, and I eat a ton of saturated fat.”
“I eat a lot of saturated fat, and I never felt better.”
“I get a great pump at the gym. What are yout talking about?!?”
To those saying, the above, I ask you your age. If you are under 40, you can still pump out enough endothelial nitric oxide to more than compensate for the negative effects of a saturated fat meal. But guys in late middle or early senior age will usually know what I am talking about. Eating a high fat meal can hit them right below the belt.
1. HACK: Walnuts Needed to Reduce Loss of Arterial Flexibility from Saturated Fat. “Tests showed that both the olive oil and the walnuts helped to reduce the sudden onset of harmful inflammation and oxidation in arteries that follows a meal high in saturated fat…However, unlike olive oil, adding walnuts also helped preserve the elasticity and flexibility of the arteries, regardless of cholesterol level. Arteries that are elastic can expand when needed to increase blood flow.” 
2. STUDY: High Saturated Fat Meal Lowers Vasocactivity (and a Low Fat Meal Did Not). Remember that vasoactivity refers to the ability of the arteries to relax and lower blood pressure and increase blood flow. “Flow-dependent vasoactivity decreased from 21 5% preprandially to 11 4%, 11 6%, and 10 3% at 2, 3, and 4 hours after the high-fat meal, respectively (all p <0.05 compared with low-fat meal data). No changes in lipoproteins or flow-mediated vasoactivity were observed after the low-fat meal…These results demonstrate that a single high-fat meal transiently impairs endothelial function. These findings identify a potential process by which a high-fat diet may be atherogenic independent of induced changes in cholesterol.” 
NOTE: In some of these studies you will researchers reference a “high fat meal” rather than a “high saturated fat” meal. However, keep in mind that, generally speaking, this are referring to the same phenemenon, because other research has shown that polyunsaturated fats and omega-3’s do not decrease nitric oxide, blood flow or endothelial function.
4. STUDY: Healthy Patient Crossover Feeding – Effects Within Two Hours. “In this study, we showed an effect (decrease) on vascular endothelial function only 2 hour after a single HF meal. Forearm BF response after vascular occlusion was 25% lower in the HF meal versus the LF meal. Skin BF response after vascular occlusion was 20% lower in the HF meal versus the LF meal. Therefore, we suggest that cardiovascular impairment, potentially, can start immediately after a single HF meal ingestion.” 
5. STUDY: Reduced Nitric Oxide Independent From Cholesterol. The title of this study says it all:
“Cholesterol-independent endothelial dysfunction in virgin and pregnant rats fed a diet high in saturated fat.”
Researchers found that “endothelial dysfunction was attributable to a reduced nitric oxide component of relaxation in VHF [very high fat] rats, and blunted prostacyclin and endothelium-derived hyperpolarizing factor components in PHF rats.” 
6. STUDY: Dieting with Lower Fat Improves Blood Flow; Low Carb Makes It Worse. “After 6 weeks, the percentage of flow-mediated dilation improved in the LF [Low Fat] diet but was reduced in the LC [Low Carb] diet versus baseline. Dilation to nitroglycerin and lipid panels was similar at 0, 2, and 6 weeks. Despite similar degrees of weight loss and changes blood pressure, LF diets improved brachial artery flow-mediated dilation over LC diets. LF diets may confer greater cardiovascular protection than LC diets.”  By the way, a “low fat diet” to these researchers actually has fat levels similar to Meditteranean levels. Undoubtedly, a “true” low fat diet would have improved things even further.
7. STUDY: Similar Study Shows Even Worse Results for Low Carb. “Body weight decreased (P < 0.05) in both groups (HF: -6.6 0.5 kg, LF: -4.7 0.6 kg). Fat mass and waist circumference were reduced (P < 0.05) in the LF group only (-4.4 0.3 kg; -3.6 0.8 cm, respectively). FMD improved (P < 0.05) in the LF [Low Fat] group (7.4 0.8% to 9.8 0.8; 32% increase) and was impaired in the HF [High Fat] group (8.5 0.6% to 6.9 0.7; 19% reduction). Increases in plasma adiponectin (P < 0.05, 16 5%), and decreases in resistin (P < 0.05, -26 11%), were shown by the LF [Low Fat] diet only.” Notice that the high fat dieters lost more weight, yet still had worse blood flow results.
NOTE: Recent research has discovered even more disturing research regarding low carb diets, which you are read about here: The Potential Dangers to Some Men of Low Carb / Ketogenic / Atkins Diets. (I am NOT saying ALL men will have issues with Low Carb Diets.)
8. HACK: Caloric Restriction Needed to Reverse Endothelial Dysfunction of High Fat Diet in Mice. “Male C57Bl/6 mice were fed with normal-fat diet (fat 17%) or high-fat diet (fat 60%) for 150 days. After establishment of obesity at day 100, a subgroup of obese mice were put on caloric restriction (CR) (70% of ad libitum energy intake) for an additional 50 days. At day 100, aortic rings from obese mice receiving high-fat diet showed impaired endothelium-dependent vasodilation in response to acetylcholine (ACh). Caloric restriction reversed high-fat diet-induced endothelial dysfunction.” 
9. Dose Dependent Increase in Cholesterol Associated with Drop in Endothelial Dysfunction. Although saturated fat does not raise cholesterol by as much as some claim, it does raise cholesterol levels and this study found that “there was a negative correlation between total cholesterol levels and maximal endothelium-dependent vasodilation (total cholesterol).” 
10. STUDY: Impaired HDL and Endothelial Function. “Consumption of a saturated fat [meal] reduces the anti-inflammatory potential of HDL and impairs arterial endothelial function…These findings highlight novel mechanisms by which different dietary fatty acids may influence key atherogenic processes.” 
11. HACK: Exercise Protects Against the Endothelial Dysfunction Following a High Fat Meal. “These findings suggest that a single aerobic exercise session cannot only counteract the postprandial endothelial dysfunction induced by the ingestion of a high-fat meal, but also increase brachial artery FMD in apparently healthy adults.”
CONCLUSION: I could go on and on with more studies showing this, but these 10 should be enough for anyone to get a good idea what is going on.
Why isn’t the word getting out? Well, my theory is that none of the major Paleo or Low Carb bloggers admit the NO-hammering effects of higher fat meals from what I can tell. In fact, I see quite the opposite where some of these sites make half-hearted attempts to try to refute the mountain of reseach that show the exact opposite of what they are saying.
In fact, one of the studies that I deliverately left out was the “Cake and Shake Study” that showed that coconut oil lowered blood more than safllower oil. One group, who shall remain nameless, had an article that went to great and laborious pains to try to explain away the fact that these Cake and Shake researchers found what several dozen others have, i.e. that saturated fat literally stuns or numbs arteries for hours after a meal. And the danger is that, unless you are very carefully doing the HACKs above, you are leaving your arteries in that less flexible and vasoreactive state which is associated with the buildup of plaque (atherosclerosis). In fact, it is even worse than that, because significant saturated fat causes the cells in your blood to tend to clump together, literally “sludging” arteries.
The bottom line is that, if you want to eat a bunch of saturated, then you won’t hear me preaching at you. Eating is religious, and I certainly don’t want to argue with anyone about it. The only thing I ask is that you don’t try to convince me that it won’t affect your nitric oxide and blood flow… flow…
2) Amer J of Cardiology, Feb 1 1997, 79(3):350 354, “Effect of a Single High-Fat Meal on Endothelial Function in Healthy Subjects”
3) Arterioscler Thromb Vasc Biol, 2005 Feb, 25(2):406-10, “Acute Effect of High-Fat Meal on Endothelial Function in Moderately Dyslipidemic Subjects”
4) ADA Diabetes Pro, 2008, “Can a Single High-Fat Meal Impair Endothelial and Autonomic Function?”
5) The Journal of Physiology, 8 SEP 2004, 517(2), “Cholesterol-independent endothelial dysfunction in virgin and pregnant rats fed a diet high in saturated fat”
6) Heart Vessels, 2010 May, 25(3):254-62, “Caloric restriction reverses high-fat diet-induced endothelial dysfunction and vascular superoxide production in C57Bl/6 mice”
7) Circulation, 1997, 96:3287-3293, “Endothelial Dysfunction Is Associated With Cholesterol Levels in the High Normal Range in Humans”
8) Nutrition Journal 2011, 10:8, “Improvements in vascular health by a low-fat diet, but not a high-fat diet, are mediated by changes in adipocyte biology”
9) J Am Coll Cardiol, 2006 Aug 15, 48(4):715-20, “Consumption of saturated fat impairs the anti-inflammatory properties of high-density lipoproteins and endothelial function”
10) European Journal of Applied Physiology, Oct 2006, 98(3):256-262, “The effect of acute exercise on endothelial function following a high-fat meal”