Saturated fat, as an all-inclusive category, has not yet been shown to beneficially or adversely affect heart health. That being said, polyunsaturated and monounsaturated have been shown to improve heart health. So saturated fats are worse relative to the unsaturated fats, but they are not bad at all.
All major studies on saturated fats merely look at what people ingest, which are common long chain saturated fats through common foods. It is wholly possible that some saturated fats can be beneficial for heart disease prevention and this just wouldn't show when you ask people what they eat (due to, say, low consumption of coconut oil in society)
A saturation of a fatty acid (saturated, unsaturated, polyunsaturated) simply refers to how many double bonds are in the fatty acid chain. Saturated fatty acids are 'saturated' with hydrogen atoms (and have no double bonds) whereas monounsaturated have one double bond and polyunsaturated have many.
As a class, saturated fatty acids are straight chain (as double bonds bend the structure).
What are the Saturated Fats?
Since the only factor that can distinguish one saturated fat from another is the length of the side chain, there are a limited amount of them. They tend to be grouped in accordance to whether their side chain is 'short', 'medium', 'long' or 'very long' in a somewhat arbitrary manner.
Short Chain are:
Butyric Acid (found in dairy)
Caproic Acid (found in dairy)
Caprylic Acid (coconut, palm kernel)
Capric Acid (coconut, palm kernel)
Lauric Acid (coconut, palm kernel)
Myristic (many sources)
Palmitic (many sources)
Stearic (many sources)
Arachidic (peanuts), not to be confused with Arachidonic acid
Some saturated fats may have different effects than other saturated fats, like like how some polyunsaturated fats (omega3) have different effects than other polyunsaturated fats (omega6). Since 'saturated fat' is a category, it is difficult to make an ultimate conclusion that applies to all saturated fats.
Saturated fat is most looked at, in regards to health, for its influence on heart disease through interacting with cholesterol and plasma triglycerides.
Several meta-analysis have been conducted on saturated fat and risk of heart health.
Looking at reviews and meta-analysis' of controlled trials, there does not seem to be much evidence that saturated fat increases risk for Cardiovascular Diseases. However, replacing some saturated fat with polyunsaturated may reduce risk.
Ones on epidemiology find relative risk ratios (RRs) very close to a value of 1, which is no effect; this suggests that there doesn't seem to be a strong relationship between saturated fat intake and risk for various conditions such as Cardiovascular Disease, Stroke, and Coronary Heart Disease. The last study there has had its statistical analysis criticized, however.
Effects on cholesterol levels
Saturated fats do increase cholesterol levels relative to polyunsaturated fats. It should be noted that in any study done on macronutrients (fat, carbs, or protein) removal of a macronutrient must be met with inclusion of another in order to balance calories out. Many studies replace saturated fats with polyunsaturated fats, which tend to reduce cholesterol and triglyceride levels. This may lead to the conclusion that saturated fats raise them, when the possibility that they are inert is viable.
Diets high in monounsaturated fats also tend to be beneficial for certain parameters of heart health.
It should be noted that causation has not yet been placed on (dietary) cholesterol for causing heart problems, it is definitely correlated, with the ratio of HDL cholesterol to Total cholesterol being the strongest predictor.
At least one study has noted that substituting dietary monounsaturated fatty acids with saturated fats via vegetable oils (40% fats overall, 16% of the chosen fat in each group) was associated with slightly more anger in participants, although this study also noted a spontaneous decrease in activity which may have contributed.
Food intake underlies a great deal of weight gain or loss, and thus things that may modify food intake can indirectly modify weight changes.
When looking at neuropeptide YY (a hormone that suppresses appetite), it is known that fats per se are more effective than carbs and possibly proteins at increasing it after a meal. When looking at what fats are consumed saturated fats seem comparable to PUFAs (but greater than MUFAs) in increasing it according to one study while other studies note either comparable effects or an unreliable increase in saturated fat versus MUFA (no changes in whole day values, but following a meal there was a spike).
In regards to the neuropeptide YY (which suppresses appetite), saturated fats may be more effective than unsaturated fats at increasing it but the results are pretty unreliable and the magnitude of effect is not too large
When looking at studies that directly measure hunger and fullness, saturated fat appears to be associated with less hunger relative to PUFA and MUFA or there are no significant differences between groups either with dietary intake or direct infusion of saturated fats into the duodenum.
Saturated fats either result in less food intake and appetite or they do not differ from unsaturated fats
Switching dietary MUFAs out for saturated fatty acids in otherwise healthy young adults appears to decrease spontaneous activity levels.
It is known that diet interacts with androgen levels (known to be related to reduced androgen concentrations in vegetarians and reduced androgen levels in cohorts with lower fat intakes), which is thought to be related to dietary fat since putting men on a low-fat (high fiber) diet reduces circulating androgens whereas the opposite exists as well (higher fat diet at 41% of calories, with a higher intake of saturated fat, increasing testosterone). The magnitude of these changes is a low fat diet reducing testosterone in older men by 12% and an increase in dietary fat in young men increasing testosterone by 13%.
Acutely, there may be a slight suppression of testosterone concentrations following ingestion of a high fat meal (fatty acids not specified) which is thought to be related to chylomicrons and NEFAs (increase in serum by ingestion of dietary fat) may suppress LH-induced testosterone synthesis. Elsewhere, androgen precursors have been noted to be increased without an increase in testosterone.
Dietary fat in general (with a slight trend towards saturated fats) are known to positively regulate testosterone and androgen production. The magnitude of changes, however, are fairly small (below 20%)