science

This is where the data meets an uncomfortable impasse. Hispanics in the U.S. live a lot longer than whites. It's not because of socio-economics. Hispanics eat a lot of meat, too. It is theorised that their legume heavy diet might be responsible. Meaning that, despite eating a lot of carbs, they still live longer. I suspect longevity effects are primarily related to the fibre. This might be true in the study linked. Perhaps it isn't the low carb/low fat part which gave heart benefits, but the higher fibre intake.

As for the mechanisms:

1. Fibre binds bile acids, which increases bile acid secretion. The liver uses LDL to make more bile acid, reducing LDL.

2. Fibre acts as a glucose release modulator. Glucose spikes are responsible for a range of immediate and systemic issues. Reducing overall glucose consumption and especially spikes results in lower risk of type 2 diabetes, metabolic syndrome, and atherosclerosis progression.

3. Lower blood pressure (we're not really sure why yet).

4. Fermentable fibres are metabolized by gut bacteria into short-chain fatty acids. These reduce systemic inflammation, improve gut barrier integrity, improve insulin sensitivity, and regulate immune function. The inflammation one in particular could explain a great deal of the health benefits.

5. The cancer risk specifically decreases because of dilution and faster transit of carcinogens, SCFA production (especially butyrate, which has anti-tumor properties), and reduced insulin and IGF-1 signalling.

6. Fibre keeps you full for longer, reducing the risk of obesity.