Sunday, January 1, 2012

DGA 2011 - Total Fat and Saturated Fat: Part 1

“3.1 Limiting intake of foods and drinks containing saturated and trans fat”

“The Guidelines recommend caution in choosing foods high in fat because of the implications for weight gain and cardiovascular disease risk”

In response to this section I will show that this caution isn’t supported by the research the dietary guidelines have cited and that polyunsaturated, not saturated fats increase cardiovascular disease risk.
Dietary Fat and Excess Weight Gain

“Fat-rich foods are energy (kilojoule) dense, heightening the risk of excess energy intake [489].”

Part 1 – Fat-rich foods are energy dense

Fat is indeed more energy dense per gram than protein or carbohydrate.  Fat yields 37 kJ per gram while protein and carbohydrates yield 17 kJ per gram.  The conclusion that high fat foods are energy dense is not entirely accurate.

100 grams of Coles 3 star minced beef has 19.9 grams of protein, 15.4 grams of fat and 0.5 grams of carbohydrate.  This food would be considered ‘high fat’.  The total kilojoules come to 908 per 100 grams [1].

Cereal grains, which we are told to eat many serves of, are low in fat but very high in kilojoules.  Data from the USDA nutrient database suggests brown rice contains 1515 kJ per 100 grams.  The kilojoules in brown rice come from 7.5 grams of protein, 2.68 grams of fat and 76.17 grams of carbohydrate, of those carbohydrates 3.4 grams are dietary fibre.  Other cereal grains have roughly 1400-1650 kJ per 100 grams with minor differences in protein, fat and carbohydrate.  The exception among cereal grains is corn, which contains 360 kJ per 100 grams [2].

Many foods considered to be high in fat, such as the 3 star minced beef, aren’t recommended by the dietary guidelines on the basis that they are too energy dense.  Yet at the same time, the same guidelines recommend cereal grains to be the basis of our diets, despite grains are more energy dense than most foods and more energy dense than many ‘high fat’ foods.

Part 2 – Fat-rich foods heighten the risk of excess energy intake


The study made several findings that initially appear to contradict each other:

The rates of obesity has increased, while the proportion of dietary fat has decreased.

“However, obesity rates have increased despite of decreasing intakes of fat, which suggests that factors other than dietary fat may play a more important role in the increasing prevalence of obesity”

Populations who report eating more fat are more likely to be overweight.

“The vast majority of cross-sectional and cross-population studies – performed with a variety of methodologies, in multiple countries and in various age groups over the last 15 years – continue to show a correlation between higher fat intake (usually reported as percentage of caloric intake, but often also as total fat intake) and increases in weight”

The results of the clinical trials, suggest those on both low carbohydrate, high fat diets and low fat, high carbohydrate diets spontaneously reduce calories and lose weight.

Low carbohydrate, high fat studies:

“Many smaller intervention studies examining the effect of dietary composition on weight loss have found that the lower carbohydrate, higher fat diets (based on the AtkinsTM diet which is designed around limitation of dietary carbohydrate) often lead to more weight loss than either low fat or more traditional weight loss diets.”

“A meta-analysis of randomized controlled trials of low carbohydrate diets ( ! 60 g carbohydrate per day) without energy restriction versus low fat diets ( ! 30% of total calories from fat) with energy restriction revealed greater weight loss at 6 months for the low carbohydrate diets, although there was no significant difference at 1 year. It should be noted that the excess weight loss in the low carbohydrate diets has been attributed to a greater caloric reduction, and that the difference in weight loss is greatest at 6 months”

“A more recently reported meta-analysis of 5 trials (n = 447 subjects) comparing the effect of low carbohydrate diets (without energy restriction) to low fat diets (with energy restriction) found no difference in weight loss between the 2 treatments after 1 year, although the low carbohydrate diets were more effective at 6 months (weighted mean difference 3.3 kg).”

Low fat, high carbohydrate studies:

“Nonetheless, the low fat cohorts had significantly, albeit modestly, greater weight loss at 3–6 years of intervention (with a difference between groups of 0.8–1.3 kg). However, the aim of the intervention was prevention of cancer with no focus on caloric restriction or weight loss, and the participants were encouraged to maintain their body weight. The weight loss can therefore be regarded as unintentional, and brought about by the ability of the low fat diets to reduce caloric intake per se, without any attempt to do so”*

“A meta-analysis of 16 trials comparing ad libitum low fat diet to habitual diet or moderate fat diet ad libitum found that a reduction in dietary fat without a prescribed restriction in calories resulted in more weight loss where the group difference was 3.2 kg”

“Other, prospective randomized studies have shown an ad libitum, low fat, high carbohydrate diet to be superior to a fixed energy intake for maintaining weight after a major weight loss.”

The studies that looked at low carbohydrate, high fat diets had other experimental groups to compare low carbohydrate, high fat diets with other diets, such as low fat, high carbohydrate diets.  The studies supporting low fat, high carbohydrate diets tend to be only compared to a calorie restricted control group and one study (*) did not have an equally matched control group.

*“A systematic review of dietary weight loss controlled trials suggests low fat calorically restricted diets are associated with significant and sustained weight loss; however, the control groups in the reviewed studies are not well matched, making specific conclusions on the role of total fat per se impossible.”

Low carbohydrate, high fat diets and low fat, high carbohydrate diets spontaneously reduce calorie intake and are successful in weight loss trials.  This suggests neither macronutrient by itself is responsible for excess weight gain.

“Thus, the data from intervention studies are again inconsistent and therefore inconclusive on the role of total fat and weight regulation. Studies comparing the Atkins diet to other diets (with percentage of fat being the primary difference) and similar overall intensity of intervention tend to show a greater weight loss than lower fat diets. However, the differences in other macronutrients, and the high drop out rate limit these results.”

A possible explanation for this apparent paradox is that people respond differently to different diets, which may depend on their degree of insulin sensitivity.  This finding is contrary to the goals of a one-size-fits-all dietary guideline, but rather should inspire dietary guidelines that recommend universal principles such as improving food quality, rather than macronutrient ratios.

“Another consideration rarely accounted for is baseline physiological status or genetic variation. For example, some studies have shown that when participants are stratified by baseline insulin sensitivity, those that are more insulin resistant tend to lose more weight on a higher fat diet than those who are more insulin sensitive”

Another possible explanation is that junk food (pizza, baked goods, chips, etc) promotes weight gain.  Junk foods tend to be low in protein, high in fat, high in carbohydrates, very low in nutrients and are highly palatable.  People eating low protein diets (under 15% of total calories) have an increased appetite as a mechanism to eat sufficient protein [3], it’s also likely this mechanism applies to micronutrients as well.  Many micronutrients support mitochondrial function.  Mitochondrial dysfunction therefore obesity can result if there are not sufficient nutrients [4].  Junk food may also contain artificial trans fatty acids (TFA), which can increase weight gain without changes in calorie intake (see below for SFA, natural TFA and artificial TFA).  Restricting either fat or carbohydrates reduces the potential for junk foods to enter in the diet.  .  A low fat dieter would restrict junk food due to it being high in fat, a low carbohydrate dieter would restrict junk food due to it being high in carbohydrate.

When junk food is reduced in the diet other food would replace it.  The replaced food would be higher in protein and micronutrients so both diets improve their food quality.  With more nutrients in their diet both the low carbohydrate and low fat dieters wouldn’t feel compelled to overeat to compensate for nutrient poor junk food, and therefore lose weight.  Fewer artificial trans fatty acids in the diet – a consequence of reducing junk food – would also improve conditions such as obesity, the metabolic syndrome, cardiovascular disease and many more.

Food quality could explain the observations mentioned in the study.  Obesity has increased from 15.0% in 1976-180 to 34.3% in 2007-2008 and extreme obesity has increased from 1.5% in 1976-1980 to 6.0% in 2007-2008 [5].  Meanwhile average yearly consumption of added fats was 66% higher in 2000 than in the 1950s (in this period consumption of butter, lard and beef tallow decreased so the increase was mostly from vegetable oils), grain consumption was 45% higher in 2000 than in the 1970s and consumption total caloric sweeteners was 39% higher in 2000 than in the 1950s.  This corresponds to a 24.5% increase in calories consumed between 1970 and 2000 [6].  People eating high fat diets tend to be fatter, but these people aren’t usually as health conscious, ignoring the message to eat less fat while also ignoring the messages to eat healthily, exercise, drink in moderation and not smoke [7].  These confounding variables and other unknown ones may influence the data in such a way that the results are skewed even after correction.  Another explanation is that those who are health conscious underreport their fat consumption, based on the social judgement that dietary fat is unhealthy [8].

“Finally, when interpreting the results of epidemiological studies, one should be mindful of control for potential covariates such as age, physical activity level, smoking status, BMI or other measures of adiposity, consumption of alcohol and use of hormonal contraceptives. As in the case of dietary records, methods of estimating physical activity level are prone to reporting errors.”

From the study cited in the dietary guidelines it would appear neither fat nor carbohydrate is uniquely fattening.  The alternative hypothesis suggests nutrient intake and food quality are major determents of weight loss, rivalling caloric restriction without the difficulty of deliberately restricting calories.

Foods high in fat aren’t necessary energy dense.  Both low carbohydrate, high fat diets and low fat, high carbohydrate diets result in spontaneous calorie restriction and weight loss, which may be due to the improved food quality of both diets from the reduction of junk food.  This also suggests both fat and carbohydrate alone aren’t uniquely fattening.  Therefore the claim the high fat foods increase the risk of weight gain is unfounded based on the referenced scientific literature.

However, this is not what is mentioned in the dietary guidelines when the 489 study is cited.

“Fat-rich foods are energy (kilojoule) dense, heightening the risk of excess energy intake [489].”

There’s only one part of the study that is relevant to what is said in the dietary guidelines.

“At least one randomized trial comparing the effects of fat intake on weight regain has demonstrated lower weight regain in those randomized to the low fat diet, due to a lower total energy intake.”

However, we know from this study that low carbohydrate, high fat and low fat, high carbohydrate diets result in spontaneous calorie restriction.  This effect can’t be attributable to dietary fat and a lower total energy intake can also be achieved on a low carbohydrate, high fat diet.

The 489 study was referenced repeatedly for the same purpose.

“Reducing the amount of dietary fat will not necessarily reduce dietary energy, but it is prudent to choose low-fat and low energy-density foods in a total dietary pattern that seeks to control overall energy intake. Because of this total energy effect, there are difficulties in appraising research on the effect of dietary fat alone on weight gain [489] (see Chapter 4).”

“Fat is an energy-dense macronutrient, so consumption of excess fat may lead to excess energy (kilojoule) intake and weight gain [489]”

But that was not the conclusion of the cited study.

“Thus, the data from intervention studies are again inconsistent and therefore inconclusive on the role of total fat and weight regulation. Studies comparing the Atkins diet to other diets (with percentage of fat being the primary difference) and similar overall intensity of intervention tend to show a greater weight loss than lower fat diets. However, the differences in other macronutrients, and the high drop out rate limit these results.”

A thorough reading of the study contradicts its misuse in the dietary guidelines.

You can read Part 2 here

2 comments:

  1. That is fantastically well written Steven. I hope that you are going to submit it. I look forward to reading the rest of your posts. Cheers Peter

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    1. Thanks Peter. I just made a page called DGA 2011 which has links to my other responses. I will be making a submission which I'll finish and put on my blog closer to the end of February.

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