There are healthful and harmful fats and healthful and harmful carbohydrates. It makes no sense to try to restrict either most fats or most carbohydrates. You need soluble fiber and resistant starch carbohydrates to help prevent heart attacks and prolong your life, and you also need monounsaturated and polyunsaturated fats to help prevent heart attacks, certain cancers and premature death.

A Japanese study followed 34,893 men and 46,440 women, 35-69 years of age, for nine years and found the highest death rates were in men on low-carbohydrate diets and women on high-carbohydrate diets (J Nutr, 2023 Aug;153(8):2352-2368). This can be explained by the fact that men are usually larger and more active than women and need more calories. When they eat a low-carbohydrate diet, they make up for their calorie needs by eating far more meat and saturated fats that increase risk for coronary artery disease and premature death. Women on high-carbohydrate diets ate more refined carbohydrates and sugar-added foods, which cause a higher rise in blood sugar that is associated with increased risk for diabetes, heart disease and premature death. This confirms what we already know. It is harmful to your health to eat:
• high fat and saturated fat diets that increase risk for heart attacks and strokes
• sugar-added foods and drinks and refined carbohydrates that can cause high rises in blood sugar, which can damage cells throughout your body.

Eating for Longevity
Current studies are confirming studies done over the past 60 years, which have shown that consuming mammal meat, saturated fat, sugar-added foods and drinks, and other refined carbohydrates are associated with increased risk for many diseases. This Japanese study is important because several popular diets recommend severely restricting carbohydrates or fats, and this can harm you. For example, keto diets recommend severe carbohydrate restriction, and you need fiber and resistant starches found with carbohydrates. Low fat diets recommend restricting all fats, but you need unsaturated and monounsaturated fats to meet your needs for nutrients and calories. Monounsaturated fats and polyunsaturated fats help lower LDL cholesterol, while saturated fats may increase heart attack risk.

Increased total carbohydrate intake was not associated with increased risk for heart disease. Eating plants (a source of carbohydrates) is associated with reduced heart attack and stroke risk, while eating sugar added to prepared foods and drinks is associated with increased heart attack and stroke risk (BMC Med, Feb 14, 2023;21(1):34).

You Need the Healthful Carbohydrates
Carbohydrates are composed of chains of sugar molecules. They are found in all plants and all foods made from plants. Carbohydrates can be a single sugar, or two, three or more sugars bound together. Thousands of sugars bound together are called starch, and millions of sugars bound together so tightly that you cannot break them down are called fiber. A review of the literature found that high carbohydrate, plant-enriched diets are far more effective in long-term weight control and diabetes control than severe carbohydrate restriction as in keto diets (JAMA Oncol, 2022;8(8):1201-1208; PLoS One, 2015 Apr 21;10(4):e0126104; BMJ, 2020 Mar 18;368:m688; Am J Clin Nutr, 2018;107:257-267).

Only single sugars can pass from your intestines into your bloodstream. When you eat, food that contains starch enters your intestines where enzymes knock off each end sugar consecutively, and each end sugar is absorbed immediately. All simple sugars and starches that are broken down in your intestines go into the bloodstream rapidly, which causes blood sugar to rise. Fiber and other resistant starches contain long chains of sugars that cannot release their end sugars, so they are not absorbed. They pass to the colon where bacteria convert them into short chain fatty acids (SCFAs) that help to prevent colon cancer and heart attacks.

A healthful diet has lots of carbohydrates that release their sugars slowly, and only small amounts of carbohydrates that release sugars rapidly. The easier it is to break carbohydrates down into single sugars, the higher your blood sugar level rises and the more insulin you produce. Most refined carbohydrates are ground-up whole grains (flour) or sugars that have been extracted from high-sugar plants (sugar cane, sugar beets, corn, fruits and so forth). The most healthful carbohydrates are those left with fiber where nature puts them: in whole grains, beans, nuts and other seeds, vegetables and fruits.

My Recommendations
Most recent literature on the subject confirms that either loading on or severely restricting carbohydrates, fats or proteins can harm you. I recommend that your diet should concentrate on:
• eating a wide variety of fruits, vegetables, whole (unground) grains, beans, nuts and other seeds
• restricting mammal meat, processed meats, non-fermented dairy products, eggs, sugar-added foods and deep-fried foods
• avoiding sugared drinks, alcohol, and tobacco.