- Limit foods with a high content of saturated fat and cholesterol. Substitute with grains and unsaturated fat from vegetables, fish, legumes and nuts.
- Limit cholesterol to 300 milligrams (mg) a day for the general population, and 200 mg a day for those with heart disease or its risk factors.
- Include fat-free and low-fat dairy products, fish, legumes, poultry and lean meats.
A study was published last year in the American Journal of Clinical Nutrition (November 2005) that followed a group of 86-men, aged 22-64 eating three different diets. Meals were prepared for them to maintain compliance with the dietary changes and the fat content of each diet was manipulated by using different dairy products - full-fat, reduced fat and non-fat.
The results are quite telling about how saturated fats and our intake of dietary cholesterol affect our cholesterol.
Before we look at the findings, let's see what the diets looked like:
The "Average American Diet" (ADD)
- 36.8% fat (14% SFA, 14.5% MUFA, 8.3% PUFA)
- 49.6% carbohydrate
- 13.6% protein
- 104mg cholesterol/1000 calories
The "Step I Diet"
- 28.1% fat (8.8% SFA, 11.5% MUFA, 7.9% PUFA)
- 58% carbohydrate
- 13.9% protein
- 76mg cholesterol/1000 calories
The "Step II Diet"
- 23.7% fat (6.2% SFA, 9.7% MUFA, 7.8% PUFA)
- 61.9% carbohydrate
- 14.4% protein
- 63mg cholesterol/1000 calories
All participants were fed an isocaloric diet to maintain their weight and the calorie levels ranged from 2200-3400 since each participant ate what they needed to maintain their weight. If their weight fluctuated more than 1kg, their diet was adjusted until their weight returned to their intial weight. This is an important factor in this study - the men were neither allowed to gain or lose weight during the intervention periods. What this allows is a clean look at how dietary fat is impacting various measures of health without the confounding variable of weight change.
At baseline, the men had an average
- Total Cholesterol = 186.34
- LDL Cholesterol = 126.41
- HDL Cholesterol = 40.20
- Triglycerides = 96.57
- TC/HDL Ratio = 4.63
And, let's be clear - these guys were pretty average...the average BMI was 25.6 (range was 22-33.2)
Wonder what each diet did to their cholesterol levels? Well, you might be surprised....
The Step II Diet (the one you might think was the healthiest) did the worst, even though it effectively lowered total cholesterol the most, from 186.34 to 169.71. LDL was reduced from 126.41 to 110.95, but HDL was also reduced from 40.20 to 36.72 and triglycerides rose from 96.57 to 108.09.
The Step I Diet fared slightly better, but still wasn't an improvement when we take a close look. Total cholesterol declined from 186.34 to 177.44 with LDL decreasing from 126.41 to 117.13 - but again, the diet also took it's toll on HDL, causing it to decrease from 40.20 to 38.27. Triglycerides also rose from 96.57 to 106.32.
The real surprise was that the ADD diet actually made some improvements in cholesterol. Total cholesterol remained 186.34, but LDL declined slightly to 125.64 and HDL rose from 40.20 to 41.36, while triglycerides declined from 96.57 to 93.91.
The researchers did a number of analysis - in the hope to find some redeeming value for the low-fat diets - to no avail. No matter how hard they looked, no matter what parameter they analyzed (from BMI to glucose, from insulin to waist circumferance, from body fat percentage to HOMA score) the lower fat diets performed poorly.
You wouldn't know that from the abstract though - in it the researchers merely conclude "Persons who are insulin resistant respond less favorably to Step II diets than do those who are insulin sensitive."
Noteworthy in the full-text of the paper is this observation from the researchers - "Being overweight and the associated insulin resistance that can lead to the metabolic syndrome is a growing health problem. Only 7% of our study population met the criteria for having metabolic syndrome as defined by National Cholesterol Education Program. Nonetheless, the participants who were overweight or who had higher insulin concentrations had altered metabolic responses to lower fat diets. Thus, the effects of elevated insulin concentrations on the LDL-cholesterol and triacylglycerol responses preceded the development of overt metabolic syndrome."
It's estimated that 25% of Americans already are affected by the features of Metabolic Syndrome - this particular study only had 7% within its subjects, and yet - even before they met the criteria for Metabolic Syndrome - if they were overweight and had higher insulin concentrations, the Step I and Step II Diets were bad news for their cholesterol!
If you recall, this was published in November 2005 - just three months ago. This month we had the Women's Health Initiative Dietary Modification Trial show that low-fat diets did not improve cholesterol or reduce the risk of breast cancer, colon cancer or cardiovascular disease. There are many other studies out there too that have resulted in similar findings. Yet, the AHA and others continue to march to the beat of dogma instead of evidence-based standards.
In an editorial regarding this study, the author, Jose Ordovas, notes this when he wrote "These results were, on average, similar to those from many previous studies that used similar experimental designs and diets."
Ordovas continues later with "The other relevant outcome of the study relates to the results obtained for the ratio of total to HDL cholesterol, also known as the atherogenic ratio. Higher values have been associated with an increased CVD risk. Therefore, the elevations observed after the Step I and II diets cast some concerns about the efficacy of these low-fat diets to reduce CVD risk."
He then quickly retreats however, and instead looks to call the study design into question "However, experimental design may have been the driving force for the increased ratio of total to HDL cholesterol and triacylglycerol concentrations observed after the low-fat diets," even though he'd previously praised the design earlier "Lefevre et al's study design fulfills many of the expectations of a well-conducted dietary intervention study, namely, a randomized, double-blind, 3-period crossover controlled feeding design. In addition, these investigators take multiple measurements per dietary phase, which reduces the confounding of intraindividual variability. Moreover, they chemically measured the menus provided, thereby connecting the calculated with the actual composition of the diets."
He ends by saying that "the first baby steps can be seen already in the most current version of the US Department of Agriculture pyramid (www.mypyramid.gov). Perhaps at some time in the future, the current controversies will be put to rest. We will be able to identify those persons for whom diet plays no major role in their risk of CVD and this should appease those who defend the diet-heart null hypothesis. The same tools will identify those persons who may benefit more from one of the many potentially beneficial diets currently proposed."
This leads a reader to believe that someone in the study, on the Step I or Step II Diets, actually saw an improvement in their cholesterol! There is no data to suggest such a leap of faith.
Basically, he tows the line and maintains the message that the Dietary Guidelines for Americans (DGA), which is close to the Step I Diet, is just fine and dandy.
This study, taken with the number of other studies that have reached similar findings should be reason enough to demand we cease-and-desist with these guidelines. With 25% of the adult population already presenting features of Metabolic Syndrome, such dietary recommendations will continue to exacerbate the problem, not make things better.
Folks, just look at the data for yourself - reducing your saturated fats and using "good" monounsaturated and polyunsaturated instead, even lowering your total fat - does nothing to improve your cholesterol! Using low-fat and fat-free dairy in place of whole milk dairy - that too does nothing to improve your cholesterol! Lowering your intake of dietary cholesterol - yup, that too does nothing to improve your cholesterol. But you wouldn't know that if you listen to the "experts" and don't read the data for yourself, would you?