Your post is full of the science that people no longer trust. There is plenty of evidence that fat doesn't cause weight gain or heart attacks, and that exercise doesn't lead to weight loss because it makes you hungry. I don't know the correct answer, but I know there is a lot of uncertainty now, and there seemed to be no uncertainty in the food pyramid days.
Right, and perhaps one of the biggest things to understand is that, while thermodynamics does apply to human exercise and consumption and is really easy to understand and reason about, the conclusions you get from that tend to be overly simplistic. The problem is a fallacy along the lines of "all humans are perfectly uniform, rational decision-makers." Instead different foods release different chemicals in your brain over different timelines, causing your cravings for food to be different.
Just to take the simplest case, there is something like a 20 minute delay between food hitting your stomach and any sort of satiety signal hitting your brain. So if you have an abundance of easy-to-eat food, then you may end up consuming more calories than someone who doesn't. (You could call this the "second bowl of cereal effect": when you've eaten a bowl of cereal and still feel hungry afterwards, it's because you ate too fast because you didn't want the cereal to get soggy.) Easy weight loss plan: cook your own meals, tasting along the way; by the time you're sitting down with the food you won't be quite so hungry.
And none of that picture has to do with calorie-counting. Calorie-counting is important if you can stick to it, but most people keeping informal calorie-counts will be victim to their cravings, and those cravings are dictated by parameters of the food other than the food's caloric content.
The current science does suggest eating too much fat is still bad.
EX: "The American Heart Association’s Nutrition Committee strongly advises these fat guidelines for healthy Americans over age 2:
•Eating between 25 and 35 percent of your total daily calories as fats from foods like fish, nuts, and vegetable oils."
Note both the lower and upper bound. Eating say 75% of your daily calories as fat is generally a bad idea for most people. But so is limiting yourself to 1%.
PS: This is one of those cases where oversimplification can be harmful. But, while looking at people with extremely high fat diets demonstrated a problem the translation from limit to eliminate is what most people heard.
According to that page you need to lower saturated fat to 5%-6% of calories. I'm suggesting that current science does not support the connection between saturated fat and heart disease. Nor does current science support their recommendation to cut salt. The AHA recommendations have been a dietary disaster for 30 years because they suggest that low fat food can be eaten without consequence, which has led to a massive uptake in the consumption of sugar and processed carbohydrates. And it was largely based on bad science.
> According to that page you need to lower saturated fat to 5%-6% of calories. I'm suggesting that current science does not support the connection between saturated fat and heart disease.
Studies, including recent ones, show that replacing saturated fat with polyunsaturated fat reduces cardiovascular disease risk (IIRC, in both sexes, but moreso in men than women.) Mostly, what's changed is that we now also have evidence that replacing saturated fat with trans fat or carbohydrates is, at best, no better than just staying with saturated fat.
There is probably no harm replacing saturated fat with polyunsaturated fat, but that's not what happened based on decades of AHA and govt. recommendations. What happened was that people replaced saturated fat with simple carbohydrates and trans fats, got fat, and had heart attacks. Take a look the heart safe foods the AHA currently approves. Bagels, rice, tortillas, orange juice, potatoes, cheerios. It is a recipe for obesity and illness.
You can't just pigeonhole fats into three categories and be done.
Butyric acid and stearic acid are both saturated fatty acids, but they serve very different roles in the diet. Similarly, ALA and LA are both essential unsaturated fatty acids, but they compete for the same desaturating and lengthening enzymes in the body. So if you eat sufficient quantities of those fatty acids in the wrong ratio, you can still see symptoms of dietary deficiency. And different people produce different quantities of those enzymes or different variations with greater or lesser effectiveness.
The AHA made insufficiently informed recommendations, and the nonscientific population followed them, often by replacing animal-based fats with vegetable-based fats with vastly different fatty acid ratios.
These were sometimes chemically treated to turn them into trans-fats, which in a key-keyhole model of body chemistry is like bending a kink into the key to your front door, then jamming it into the lock with a hammer and forcing it with vise-grips every time you wanted into your house. The trans fats resembled saturated fats enough to be used in the same way, but that kink in the key would cause persistent damage.
And foods manufacturers also replaced fats with sugars and sodium salts, which caused different problems.
Different foods have different fat profiles, just as they have different protein profiles. Eggs and milk have amino acid ratios that very closely match what humans need, whereas beans and rice are insufficient in isolation, but complete in combination. Similarly, beef suet, pork lard, olive oil, coconut oil, and soybean oil have different fat profiles.
We still don't know what the "best fat" food is, like we know that poultry eggs are very nearly the "best protein" food. And "fat quality" might not even be as homogenous between individuals as it is for the amino acids.
Any recommendations at this time are almost certainly unfounded or unsupported by rigorous and repeatable research. You really have to do your own homework on this one, and avoid making any conclusions based on insufficient evidence.
> There is probably no harm replacing saturated fat with polyunsaturated fat, but that's not what happened based on decades of AHA and govt. recommendations.
One of the leading hypotheses is that omega-6 fat - which is a subcategory of polyunsaturated - is very very bad for you. So there is absolutely potential for harm in replacing saturated fat with polyunsaturated fat.
Exercise on its own doesn't lead to weight loss (in order to burn the necessary calories, you'd have to be exercising all day long), but it is not uncommon for exercise to suppress appetite, thereby reducing the calories in component of the weight loss equation. Unless of course hunger signals are being ignored, as in the case of unconscious, binge, or comfort eating.
> Exercise on its own doesn't lead to weight loss (in order to burn the necessary calories, you'd have to be exercising all day long)
Assuming that you were in perfect calorie balance before, any additional exercise without additional calorie consumption will produce a calorie deficit. This may or may not produce weight loss depending on the exercise profile and a lot of other factors (including, IIRC, what and when you eat relative to when and how you exercise), since its possible to gain weight with a calorie deficit while if you are building muscle fat enough (since fat stores more energy per unit mass than muscle.)
To be sure, there are many factors. But going by what a lot of people do, they will get a workout of thirty minutes burning maybe 200-300 calories, then reward themselves with a Big Mac at 550 calories, and they probably already had a caloric intake in excess of maintenance (hence why they are exercising to lose weight, and more likely to go for that reward). Heck, even one Snickers[1] bar can counteract that workout. Not saying this is everyone, but it seems to be a common pattern: most people don't realize they need to control their intake, even if they don't reduce it, otherwise all the exercise in the world won't lead to weight loss.
> But going by what a lot of people do, they will get a workout of thirty minutes burning maybe 200-300 calories, then reward themselves with a Big Mac at 550 calories,
The effect of exercise plus an additional Big Mac does not reinforce the claim that "exercise on its own doesn't lead to weight loss", because "plus a Big Mac" is not "on its own".
> and they probably already had a caloric intake in excess of maintenance (hence why they are exercising to lose weight, and more likely to go for that reward)
The reason why they are exercising to lose weight is probably that they have a current weight above their desired weight. That doesn't mean that they have a current calorie surplus -- plenty of people seek to lose weight when their current weight is stable but above their desired weight.
