Are we eating too many carbs? And do we need to switch to the primal/paleo diet?

Question

TL;DR

Accepted knowledge is that high carb low fat diet is good. Paleo diet says opposite, the claims seem solid for the Paleo diet but I am still skeptical as Science seems to think that conventional wisdom is correct but am looking to see if there are any problems with either side of the argument.

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One day I stumbled across this site.

The basic claim laid out there is this: We as humans only started eating large amounts of carbs when we got into agriculture. Even then, it's only in the last 100 years we started to put them (including sugar) into everything in large amounts. The human body was not made for this and quite a few modern diseases can be traced back to eating too many carbs (diabetes and obesity are easiest to connect to carb overconsumption).

The process in your body can be summarized like this:

1. When you eat carbs your body immediately converts them to glucose.
2. Because of the higher blood sugar levels (lots of glucose in your blood,) your body makes insulin.
3. The insulin puts your body in a state where it absorbs all glucose it can find into its cells and starts running on glucose.
4. At the same time, instead of using it, your body stores all fat that comes in.
5. The result is that, when your done eating, it won't take that long to work through your glucose stores (usually one or two hours) after which you will be hungry again. So you'll start filling up on carbs again and in this way leave the fat stores constantly growing.

The science behind this seems solid but the leading advice agencies still advise eating lots of carbs and staying low on fat and protein.

It took me a few weeks of off and on reading of everything I could find on this subject before I started to believe in the science. I was really skeptical when I read the first page, but I had a real hard time finding holes in the theory so, in the end, I gave it a try. It's been around 5 weeks now and I've lost 6 kilos, the great thing is that I have been less hungry then normal (while eating a few hundred calories less a day).

I can't find any serious problems with this diet (lifestyle). I'm hoping for some discussion on the health benefits or problems associated with this lifestyle. The most common comment is that eating more fat and protein will give you a elevated risk of heart disease. I believe its a lot more complicated then that. If you take in account the two different kinds of cholesterol (LDL and HDL?) and adjust your diet to optimize the balance between those two I think the risk of heart disease as a result of the higher fat and protein intake is negligible. The fact that you will almost definitely lose weight however will do wonders for your chances of (not) getting heart disease.

Question

To further clarify my question: the accepted knowledge is that its healthier to live on a low fat, high carb diet. The Primal or Paleo diet says its the other way around, that low carb, high fat is healthier. Science seems to think conventional wisdom is correct and a high carb, low fat diet is best. I'm looking for a skeptical look at the facts. Am I goaded into believing a pseudo diet science? Or does the claim that a low carb, high fat diet is healthier seem scientifically plausible?

I would like to end with saying this is my first contribution to this stack exchange community, so if this question has any major flaws, I would like to hear what I can do to fix them. I would also like to mention that English is not my first language so please excuse me for not being as clear and concise as I might have been otherwise, I found it hard to summarize this subject to a relatively small piece of text. :)

Answer 1

"We as humans only started eating large amounts of carbs when we got into agriculture. Even then, it's only in the last 100 years we started to put them (including sugar) into everything in large amounts."

Humans have been consuming carbohydrates well into the Paleolithic. A method known as "starch grain analysis" has been able to recover all kinds of carbohydrate residue on the teeth of paleolithic humans. Some good papers in this field are Changes in starch grain morphologies from cooking and Microfossils in calculus demonstrate consumption of plants and cooked foods in Neanderthal diets (Shanidar III, Iraq; Spy I and II, Belgium). Evidence for mortar/pestle-like starch grinding dates back 30,000 years. Furthermore, almost all the "hunter-gatherer" cultures featured in paleo diet books are not hunter-gatherers, but horticulturalists like the Kitavans (or trade with horticulturalists like the Pygmies) who get most of their calories from starch. The !Kung and other related cultures are almost pure foragers, but they gather honey quite often, braving great danger to acquire it. So while evidence is spotty, I don't think there is any way we can say our ancestors ate a low-carb diet.

I cannot comment as extensively on the insulin driving fat storage since this is not my area of study, but I will say it's a perfect example of how you can build a story that looks and sounds scientifically sound by selectively referencing studies. I was initially swayed by Taube's book, particularly since I lost weight on that diet, but since then I have added carbohydrates back in and now eat a mainly carbohydrate diet and have not re-gained. My friend Dr. Stephan Guyenet has a few articles skeptical of the insulin=fat idea that are very good and extensively reference. He also works in that field: Insulin and Obesity: Another Nail in the Coffin, 3 part series on the carbohydrate hypothesis.

Why then do diseases of civilization seem to track with the adoption of refined carbohydrates? We need to look for other mechanisms such as hyperpalatibility, lack of fiber that modulates inflammation via SCFA, LPS-induced inflammation, and other factors.

Answer 2

The Australian CSIRO has published a reasonably well-received book called "The Total Wellbeing Diet" that was based upon a number of clinical trials of overweight/obese Australian adults. From this page:

The more traditional low fat high carbohydrate diets for weight loss had been challenged by alternative dietary approaches such as very low carbohydrate (Atkins), moderately high protein (ZONE) or low glycemic index diets.

However, the emerging body of CSIRO and international research confirmed that varying the protein to carbohydrate ratio during weight loss appeared to have a number of subtle benefits which may result in greater fat loss and sparing of lean body mass.

CSIRO has conducted several of the largest studies showing that higher protein dietary patterns for weight management have metabolic advantages over high carbohydrate patterns in overweight people.

The results clearly showed health benefits and significant weight loss from a diet higher in proteins and low in fats and the Total Wellbeing Diet was born.

There is a little more information on this page describing how one of the trials was conducted. I'm not sure this is precisely answers your question, however it does provide a volume of evidence regarding the effects on weight loss of different carb/protein/fat ratios in the diets of overweight adults. Diet is obviously only one factor in the maintenance of a given BMI, however (all other factors being controlled for) it seems that moderate-protein, low-carb diet will help a person shed excess body fat faster.

Answer 3

Even discounting infant mortality, life expectancy at 15 was still only 39 years in the Paleolithic era. The US average life expectancy at 15 is around 63. (The US figure happened to be handy; the US life expectancy is 37th from the top, so it's a fairly representative figure of life expectancy in developed nations.)

Being that our modern idea of health is now longevity and health into old age rather than surviving until our kids grow up -- which is now more or less a given in more developed countries -- it shouldn't make sense that we'd still consider the same diet over other diets just because it used to work. Evolution doesn't care about the elderly, after all.